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90000 How to Ventilate a Basement | Home Guides 90001 90002 By Rebecca Mecomber Updated December 29, 2018 90003 90002 More than any other room in the house, the basement can become a repository of unpleasant odors, moisture problems, mold growth and other indoor pollutants. Unventilated basements are not only prone to musty odors and mildew, the basement is also commonly used to store household chemicals. Paints, solvents, automobile products and cleaning products slowly release chemicals into the air.In an unventilated space, these chemicals build up and produce a toxic environment. Ventilating the basement exhausts polluted or musty air and draws in fresh air from outdoors. There are two basic methods for basement ventilation: natural and mechanical, both with their advantages and disadvantages. 90003 90006 Why Ventilate 90007 90002 Due to its position below ground, moisture from the earth seeps in through the floor and walls. When this cold moisture collides with the warmer basement air, condensation develops.Excessive condensation creates a musty, sour smell and, if left to collect into pools of liquid water, stagnates or produces a breeding ground for mold and mildew spores. Some molds are toxic and hazardous to the health of the home’s occupants. The Environmental Protection Agency reports that certain types of mold, particularly black mold, can aggravate or cause allergic reactions, asthma attacks and symptoms of influenza. The EPA recommends that homeowners reduce or remove any water leaks or moisture problems, and ventilate the basement.A constant influx of clean, fresh air inhibits mold and mildew growth. 90003 90010 Natural Ventilation Method 90007 90002 Natural ventilation makes use of natural air currents, but this type of ventilation works only for basements with windows that are strategically placed and able to open and close. While the natural method conserves energy, it does require more work. Windows must be opened at regular intervals and closed during times of rainfall or at night to prevent intruders from entering the basement.For best results, windows should be opposite each other across the basement space, following the natural drafts of the basement. A wet basement needs additional ventilation, such as fans or a dehumidifier. If the basement is continuously wet, the natural method is most likely insufficient and a more mechanical system may be required. 90003 90014 Mechanical Ventilation Method 90007 90002 Mechanical ventilation uses fans and vents to exhaust existing basement air and bring in fresh, outdoor air.This type of system may be as simple as placing small window fans in opposite windows or as technical as installing an exhaust fan with ventilation pipe. Many homeowners opt for a mechanical ventilation because of the great flexibility and automation it provides. Mechanical ventilation is a requirement for homes testing positive for radon, an odorless gas that is the leading cause of lung cancer in the United States among non-smokers. The EPA recommends that homeowners with radon in their homes consult with their state radon department for information on installing a radon mitigation system.90003 90018 Basic Installation System 90007 90002 A basic mechanical ventilation system begins with a design plan and depends largely on the size of the basement and other appliances or items in the space. For most small to moderately sized basements, a ventilation fan on one side of the basement and an exhaust fan on the other end is suitable. The fans may be permanently installed within existing window cavities, or may need dedicated openings cut through the portions of the basement walls that are above ground.The best ventilation fans include a humidity sensor for simple automation. Once the sensor detects a certain moisture content, the fans vent the air until the moisture content in the basement is reduced. The EPA suggests that homeowners maintain an environment below 60 percent humidity to inhibit the growth of mold and mildew in their basements. 90003.90000 Preventing mold when you insulate your basement 90001 90002 Basements do not have to be moldy, that is the first thing to realize. 90003 90004 90005 It’s easy to build a basement better, or to finish an existing basement correctly 90006, we just need to realize that they behave differently than above grade walls and to build accordingly to effectively deal with the humidity found underground — 90005 and by doing so , stop the conditions that promote mold growth 90006.90009 90004 Depending on the age of your home, you may have some interior basement insulation or maybe none. You may have an exterior damp-proofing spray on foundation walls but likely not a proper drainage mat and perimeter drain or basement flood prevention measures. 90009 90004 Outside upgrades are the ideal correction given the way basement walls were left exposed in the past; however, unless you have serious structural problems or plan to excavate for other reasons, that can be an enormous extra cost for an interior renovation project.It is much more affordable to deal with most humidity issues inside the building. The basement insulation solutions proposed here are for those that have no exterior protection. 90009 90002 What causes mold to grow in basements? 90003 90004 90005 Mold can grow on virtually any organic material 90006 as long as the moisture levels it likes and oxygen are present. 90009 90004 Because mold eats or digests what it is growing on, it can damage a building and its furnishings. If left unchecked, mold eventually can cause structural damage to building materials and can cause health problems — that’s why we do not want mold in our basements! 90009 90004 Specifically we can prevent damage to buildings and building contents in the basement areas, save money and avoid these potential health problems by controlling moisture, where humidity in the air condenses, and by so eliminating mold growth.90009 90004 90005 Quick Fact Check: 90006 Eliminating all mold and mold spores indoors is virtually impossible, but controlling indoor moisture and the hidden moisture within basement wall assemblies will control the growth of indoor mold. 90009 90004 According to the EPA, indoor relative humidity (RH) in homes should be kept below 60 percent — ideally between 30 percent and 50 percent, In addition to preventing mold forming, maintaining the correct humidity levels may also have a bonus effect — discouraging pests such as cockroaches, silverfish (bristletails) and dust mites from populating the man-cave! 90009 90004 So, Step one, getting a humidity meter and tracking the relative humidity level in your basement is the first part of understanding the mold problem in any home or basement.90009 90004 Compare budget options and special offers for manual humidity meters here (we’ve tried and like the ThermoPro TP 50) 90009 90004 Or if you have a 90005 Smart home 90006 or are heading that way, 90005 See here to compare humidity meters online including smart trackers and alarms and find special offers and reviews 90006 90009 90002 Where the moisture is, and where it wants to go: 90003 90004 90005 The key to building better mold free basements 90006 is to understand that there is a completely different set of challenges facing walls built below grade.90009 90004 The greatest source of moisture to contend with above grade is the warm, humid air generated by cooking, washing and simply breathing. Below grade, it is that big porous sponge called concrete that is sucking up water from the wet ground. 90009 90004 A different problem demands a different solution — wearing a raincoat will keep you dry when standing in a cold rain, but it will not keep you dry when jogging under a hot sun. And unfortunately for many homeowners, the way basements were finished for the last few decades is about as logical as jogging in a raincoat.90009 90004 Above grade, walls are designed to dry to the exterior. That is impossible below grade, but for some reason we still build as if it were. Despite the fact that interior vapour barriers in below grade wall assemblies are commonplace, frustrated building scientists insist that installing them is the worst thing you could possibly do down there. 90009 90052 Basement renovations demonstrating mold growth in internal stud wall © Ecohome 90004 Above is a photo of a basement being repaired after flooding.The mold damage you see is from longterm moisture exposure, not the one-time flooding event. This was a typical basement wall assembly, with a stud wall directly against the foundation followed by fiberglass insulation and a vapour barrier. Notice the difference between the studs against the foundation and the studs that formed an interior division wall; the vapour barrier did not protect the exterior wall from damage and mold growth. It caused the damage by prevented the wall from drying to the interior and instead sealed the moisture in.90009 90004 As one of the foremost authorities on healthy basement construction, Professor John Straube of the University of Waterloo dubbed this typical type of wall assembly a «mold incubation chamber». For further convincing on the topic, read ‘Built wrong from the start’ by Joseph Lstiburek of Building Science Corporation. 90009 90002 Better basement insulation techniques: 90003 90004 90005 The materials and design you choose are very important to prevent mold 90006 and should be appropriate for the environment they are destined to inhabit.Be very careful how and where you install wood and fiberglass insulation in basements (If you must), and be sure they will not see prolonged exposure to moisture or contact with humid surfaces if you do not want them to go moldy. 90009 90002 Spray polyurethane foam (SPUF): 90003 90004 90005 When SPUF works out, it can be one of the better performing products 90006 in basement applications. Being sprayed directly onto concrete walls, it ensures an even and total protection. SPUF has a high R value per inch, acts as an air barrier and a vapour barrier.However, it has been known to shrink after application, leaving air gaps and a lack of thermal protection. 90009 90004 Another downside to the original SPUF is that some blowing agents have a high global warming potential (GWP). For this reason, we like to explore less harmful alternatives whenever possible — though 90005 * January 2018 update: new blowing agents for spray foam virtually eliminate green house gases, read more here. 90006 90009 90004 Probably the most worrisome problem (as reported by a SPUF installer) is that there is a great temptation for installation contractors to tinker with the chemical mix a bit, giving it more volume with less material, which is more profitable for the installers.There are not a lot of reported cases of this, but when it goes wrong it goes very wrong. Personally, I would not let someone spray foam in my house without some pretty good references that I followed up. 90009 90004 All that said, here’s how to proceed if you plan to insulate a basement with SPUF: 90009 90077 90078 90005 Frame a 2×4 stud wall at 24 «centres 90006 leaving a gap of at least one inch between studs and concrete. 90081 90078 90005 Shim up bottom plates 90006 to allow for water to pass under in cases of mild flooding.90081 90078 90005 Have foam sprayed against the concrete wall 90006. The space left between concrete and studs is crucial to allow a seamless blanket of insulation to create an air and vapour barrier. Unprotected wood touching concrete will wick moisture and eventually rot. One inch of SPUF will solve your problems; four or 5 inches will reduce heat loss and save you money in the long run. 90081 90078 90005 Have insulation blown onto rim joists 90006 if it is not already done. 90081 90078 90005 Foam must be covered by drywall 90006 for fire protection.90081 90078 90005 Do not install an additional vapour barrier behind drywall 90006; latex paint will act in this capacity. 90081 90102 90103 Spray foam or SPUF being installed correctly on basement walls © Bala Structures 90004 There have been a few nightmare cases reported where a SPUF installation went very wrong and apparently made homes uninhabitable. Given the fact that application involves a wet spray that hardens on surfaces, it is very difficult to remove. 90009 90004 These reported cases are rare, but if you are at all concerned, there are alternatives to spray foam for insulating basements listed below that work well in the battle against moldy basements.90009 90002 EPS (Expanded Polystyrene), XPS (Extruded Polystyrene), Mineral wool: 90003 90004 90005 SPUF is quite expensive; so rigid insulation panels and a 2×4 wall with batt insulation can be a much more affordable option 90006 — but you need to know the right techniques for a succesful and mold-free wall assembly for a basement application — read on! 90009 90004 Rigid insulation board against concrete adds R value, breaks the thermal bridge and raises the temperature of the stud wall, which helps prevent moist air from condensing.The stud wall allows for the installation of wiring, additional insulation and drywall. 90009 90004 Drywall should be attached directly to studs, latex paint will act as a vapour retarder slowing any outward moisture migration while also allowing walls to dry inwards. 90009 90004 You may hear that EPS is somewhat moisture permeable; this is true, but only slightly so and not enough to be a problem. According to Professor Straube, two inches of EPS has a perm rating in the range of 60-75 ng, or 1-1.25 US perms, which is right on the cusp of what is defined by building code as a suitable vapour barrier (60ng and under). 90009 90004 At that level of moisture permeability, an almost immeasurably small amount of moisture will be able to migrate into the wall, but with no interior vapour barrier it will pass through harmlessly. EPS, XPS and mineral wool are unharmed by moisture, and perhaps most importantly, EPS and XPS are unlikely to provide a breeding ground for mold. 90009 90004 A polyethelene barrier can be included without causing harm (as seen below), as long as it is behind the stud wall, not in front.Specified correctly for basement Radon Mitigation, this will also act as a radon gas barrier to protect indoor air quality, and it will satisfy building inspectors who are not accustomed to seeing a wall without a vapour barrier and may not allow you to continue. 90009 90124 Radon gas prevention and remedial insulation in basements © Ecohome 90004 Note: the above diagram shows an ideal and complete basement renovation beginning with breaking and removing the existing concrete floor. Most older basements have very limited head room and owners are often reluctant to lower it even more by adding insulation to the floor.It also allows for the addition of a radon evacuation stack, which is the perforated tube and T-junction in this image. 90009 90004 By removing the concrete floor and maybe some of the dirt below it, you have room to insulate properly. Removing existing concrete is not as tough as it sounds — it can usually be smashed with a sledge hammer and removed in pieces. It does involve some hard work and heavy lifting, but the end result will not only be a more efficient and comfortable home, but a more valuable one at a time of resale and less likely to create the conditions that are best avoided — high humidity plus likely condensation points — both factors in producing a moldy, unhealthy basement.90009 90002 The ideal Basement wall assembly to prevent mold growth: 90003 90077 90078 90005 Install two inches of rigid insulation board directly against concrete 90006. It is easiest to attach it to the wall with a couple of concrete nails or even some adhesive while you frame walls. 90081 90078 90005 Frame an interior 2×4 stud wall at 24 inch centres 90006, pressed tightly against the foam panels. 90081 90078 90005 Install mineral wool batts in the cavities 90006. Mineral wool is unharmed by moisture, and if it gets wet it will retain its shape and R value when it dries; fiberglass is not so resilient.90081 90078 90005 Lastly, install drywall and paint it with a latex paint 90006 only. 90081 90102 90004 This technique of rigid and batt insulation may require a few more steps, but it can offer you a greater R value per dollar invested than SPUF and it allows you to do a lot more (or all) of the work yourself. 90009 90004 For reasons beyond just performance, we prefer mineral wool or EPS over XPS. XPS has a slightly higher R value per inch, but like SPUF, the blowing agents are exponentially more harmful, about 200 times more than EPS.90009 90002 What else helps prevent mold growing in basements? Ventilation! 90003 90004 90005 Another considerable improvement in keeping basements mold-free is to ensure adequate ventilation 90006. Whilst cracking open a window if your basement has them is fine if the humidity conditions outside are favorable, that’s pretty hard to judge; so a better alternative is to choose a good quality discounted HRV or ERV system with an automatic electronic humidity control. 90009 90004 Along with removing contaminants from the air, there are health consequences from having either too much or too little moisture in our homes.There are bacteria, viruses, moulds and mites that will show up on either end of the spectrum if your air is either too humid or too dry. 90009 90004 As the EPA say, somewhere in the range of 35 to 50% relative humidity is generally assumed to be the best for avoiding most health risks and irritants. It’s high enough that you will not have cracked furniture, chapped lips or constant nose bleeds, and it’s not too damp for comfort, condensation or heat consumption issues. 90009 90004 If you’re in an older home sat above a basement, do not panic.What we write in these pages is meant to inspire ideas and solutions, not fear and anxiety. If you feel good, your basement smells good and your windows (and walls) are not dripping, relax! 90009 90004 However, if your basement has a certain musty smell, or telltale black mildew and mold marks in corners or behind furniture, for peace of mind consider buying a hydrometer to measure your indoor relative humidity, which will cost you maybe $ 20 to $ 30 at most hardware stores. If you have an issue, and the humidity levels are off the scale, then 90005 chances are you’ve got a moldy basement even if you can not see it yet… 90006 90009 90169 90005 To be certain, get a humidity monitor and track humidity levels, see here 90006 90172 90169 Top Tips: For a healthy, mold-free & comfortable basement: 90172 90175 Further reading for basement mold prevention: 90176 .90000 Building better basements: how to insulate your basement properly 90001 90002 The most common practices currently employed for finishing basement interiors as living space rarely account for the impacts that come with the added moisture load below grade, or the amount of heat that will be lost to the ground. 90003 90002 Existing basements are typically under-insulated or not insulated at all, and if they are, they almost always trap moisture within wall assemblies.This leads to condensation, mold growth and rotting wall structures. 90003 90002 The following basement insulation techniques listed here are designed to offer the most sensible and durable options for interior insulation, exterior insulation, or ideally, a combination of both. 90003 90002 These assemblies have been designed to prevent moisture infiltration over the service life of a building, along with allowing the original moisture contained in building materials to escape without causing damage.90003 90002 Different types of insulation are included at different points in wall assemblies. For details and characteristics of different materials, see our page on choosing insulation. 90003 90012 90013 90014 90015 90016 90017 90014 90015 90002 CLICK IMAGE TO ENLARGE 90003 90022 90016 90017 90025 90026 90002 90028 Insulation on the exterior and interior, from outside to inside: 90029 90003 90031 90032 fiber cement board and parging above grade 90033 90032 3 «of mineral wool or EPS (expanded polystyrene).3 «is better, 2» will suffice 90033 90032 drainage mat 90033 90032 damp proofing spray on exterior concrete wall 90033 90032 2 «mineral wool board or EPS against interior concrete wall 90033 90032 2×4 stud wall with mineral wool batts in cavities 90033 90032 drywall with latex paint as vapour retarder. 90033 90046 90002 90003 90012 90013 90014 90015 90016 90017 90014 90015 90002 CLICK IMAGE TO ENLARGE 90003 90022 90016 90017 90025 90026 90002 90028 Interior insulation only: 90029 90003 90031 90032 mineral wool board or EPS as thermal break against concrete wall 90033 90032 2×4 stud wall with mineral wool batts in cavities 90033 90032 drywall with latex paint as vapour retarder.90033 90046 90002 90077 Note: Not having proper exterior moisture protection for this wall assembly will mean moisture will migrate inwards. Mineral wool is not harmed by moisture, but there may be additional heating and coolling loads inccured by having higher relative humidity levels. Basement dehumidifiers can help keep keep humidity levels manageable. Please see our page on retrofitting existing basements. 90078 90003 90002 90003 90012 90013 90014 90015 90016 90017 90014 90015 90002 CLICK IMAGE TO ENLARGE 90003 90022 90016 90017 90025 90026 90002 90028 Exterior insulation only: 90029 90003 90031 90032 fiber cement board and parging above grade 90033 90032 4 inches EPS 90033 90032 drainage matt 90033 90032 bituminous damp proofing.90033 90046 90111 Best practices for new basement construction: 90112 90002 Ideal performance and durability is achieved by insulating both the interior and exterior of foundation walls. This technique can increase the thermal performance of basements, reducing heat loss and operating costs. It also helps reduce the chance of interior moisture issues by raising the temperature of the first interior condensing surface, the concrete. 90003 90002 Below is a thermal image of the basement descibed above with insulation on both sides.The effective R value of this wall amounts to R40. Three inches of EPS under the slab amounts to R12.6, There is a solid financial argument that can be made for increasing that, particularly with the inclusion of radiant in-floor heat. 90003 90012 90013 90014 90015 90016 90017 90014 90015 90002 Thermal image of basement insulation and heat loss © Ecohome 90003 90022 90016 90017 90025 90026 90002 Exterior basement insulation is less common, probably due to the fact that it can be more expensive.And there are certainly less cases where insulation is installed on both sides. By insulating the exterior of basement walls we consume less interior space and prevent exposing walls to the seasonal freeze / thaw cycle known as ‘thermal shock’ that can cause the cracking of foundations. 90003 90002 Insulating basement interiors rather than exteriors can be the cheaper option were you to choose just one, particularly if they are intended to be finished living space. It can also more easily address thermal bridging issues at the tops of walls, as well as the junction between footings and foundation walls.90003 90002 As there is little consensus on basement design and materials used or the optimum level thermal performance, we fully expect there to be those that find this to be extreme and unnecessary in both durability and performance. We believe this stems from the fact that basements are currently dank and moldy, chronically under-insulated, and that we are simply accustomed paying the high cost of heating. 90003 90002 Ecohome promotes as much as possible, a philosophy of heat retention rather than heat generation.Additional costs for insulation are often negated by monthly savings, and a well designed and insulated basement will have a much longer service life without repair. 90003 90002 One of the most commonly overlooked benefits of extreme insulation in homes is heat security, as extreme weather events in cold months routinely drive residents from their homes for lack of power and heat. Homes that are better situated to retain heat can offer greater comfort for a longer period of time in such situations.90003 90142 Issues and solutions for all basement wall assemblies: 90143 90002 90003 90012 90013 90014 90015 90016 90017 90014 90015 90002 EPS spacer on bottom of framed basement walls © floodsill.com 90003 90022 90016 90017 90025 90026 90002 90028 Spacers below bottom plates 90029: Shimming up bottom plates with backer rods or chunks of foam can be an added measure of durability in the event of any interior flooding, by allowing water to pass under walls. 90003 90002 Read all about how to Stop Basements Flooding — Flood Prevention, Pumps & Alarms here 90166 90003 90002 90028 Slab floors: 90029 A large portion of heat is lost to poorly insulated basements, including below slab floors.The optimum levels of insulation below slabs varies by region and climate, but also by individual building site and soil conditions. 90003 90002 To save both money and energy, we recommend a minimum of R20 under slabs in most of Canada, at least along the Canadian / US border where most of Canadians live. Increased levels are recommended for more northern regions. Please see our pages on sub-slab insulation for more details. 90003 90012 90013 90014 90015 90016 90017 90014 90015 90002 Roxul mineral wool exterior foundation insulation © Roxul 90003 90022 90016 90017 90025 90026 90002 90028 Exterior EPS or mineral wool: 90029 Neither are harmed by moisture.With care they can be largely held in place against exterior walls with backfilling below grade, and fixed above grade with fiber cement board attached through to foundation walls. 90003 90002 90028 Drainage: 90029 Regardless of the location or amount of insulation, foundation walls should be protected from ground water, which should be directed to properly sloped and perforated drainage tiles. Any backfill against walls should drain easily, and weeping tile drains should be covered with a geotextile membrane to prevent clogging.The inclusion of a clean-out junction in weeping tiles can allow for easy long term maintenance. 90003 90012 90013 90014 90015 90016 90017 90014 90015 90002 Foundation perimeter surface drain © Ecohome 90003 90022 90016 90017 90025 90026 90002 A surface drain can be a valuable added measure of protection, as seen above on the interior and exterior insulation diagram. 90003 90002 This is highly recommended for metal roofs in particular as they notoriously shed eaves troughs as they shed snow.In the absence of eaves troughs (by choice or otherwise), roof water ends up at the perimeter of foundation walls. 90003 90012 90013 90014 90015 90016 90017 90014 90015 90002 Avoid wood to concrete connections in foundations © Ecohome 90003 90022 90016 90017 90025 90026 90002 90028 Avoid wood-to-concrete connections: 90029 Concrete foundations take five years to fully dry, and that is only if they are completely separated by exterior waterproof barriers from ground moisture and water.Without breaking the connection from dirt to porous concrete, foundation walls will never dry, and continue to wick moisture. 90003 90002 It is common practice to embed wood directly into concrete to frame window and door openings. Such practices put framing members at risk of rotting. Even with basements completely sealed at the exterior, wood will soak up all the available moisture in concrete. 90003 90012 90013 90014 90015 90016 90017 90014 90015 90002 Capillary break between footing and foundation © Delta 90003 90022 90016 90017 90025 90026 90002 90028 Capillary break: 90029 Footings are not protected from moisture at the bottom, the inclusion of a capillary break between footings and foundations prevents moisture from wicking into walls.There are dedicated membranes for this application, but 6 mil polyethylene will do the job as well, probably more affordably. 90003 90002 90028 Insulated rim joists: 90029 This is a very tricky location to successfully insulate and air seal. Spray polyurethane foam (SPUF) is one of the preferred solutions to this trouble spot. When insulating basement interiors, SPUF can be installed to meet interior wall insulation, breaking the thermal bridge of floor sill plates. 90003 90002 Another effective technique can be insetting floor joists from the exterior of the concrete to allow continuous insulation of rim joists on the exterior.90003 90002 90028 Stud wall and batt insulation: 90029 Again, we recommend mineral wool for its higher R value, recycled content, and ability to withstand moisture. However, the risk of moisture damage is much lower at the stud wall compared to against the concrete, so mineral wool could be safely substituted with fiberglass batts if desired, particularly in areas of low flood risk. 90003 90012 90013 90014 90015 90016 90017 90014 90015 90002 Liquid applied vapour barrier primer © Benjamin Moore 90003 90022 90016 90017 90025 90026 90002 90028 Interior gypsum board: 90029 Latex paint (or vapour retarder primer) is recomended as an interior vapour control layer below grade.It is most important to not include a polyethylene vapour barrier or other vapour impermeable materials that prevent walls from drying. 90003 90002 6 mil poly vapour barriers are an above grade solution intended to allow walls to dry to the exterior, that is impossible below grade. The only drying that will take place below grade will be inwards. 90003 90002 Building scientists agree that polyethylene vapour barriers on the inside of basement walls dooms them to failure. The source of moisture we need to protect against is exterior ground and concrete, not interior relative humidity.90003 90111 For help in 90028 choosing from different types of panel insulation see here 90029 and for a 90028 guide all about insulating exterior walls correctly from the outside, see here 90029 — from the EcoHome 90028 Green Building Guides 90029 90112 90002 Further reading: 90003 .90000 Is a Basement Included in the Square Footage of a Home? 90001 90002 This is the tale of two basements in otherwise comparable houses. One is a finished basement with a den, bedroom, and full bathroom. The other basement has some Sheetrock, an exposed toilet, and a painted floor. 90003 90002 The listing for the first house reflects the basement and number of bedrooms, including the one in the basement space, in its total square footage and price. 90003 90002 The second house only includes the square footage of the main floors and does not count a 200-square-foot bedroom in the basement.So, which listing correctly shows the square footage for a basement? The short answer is: both. 90003 90008 Does a basement count toward overall square footage? 90009 90002 As a general rule of thumb, listing agents and appraisers do not count a finished basement toward the overall square footage, especially if the basement is completely 90011 below grade- 90012 a term that means below ground level. 90003 90002 Whether an appraiser includes basement living space ultimately depends on which state you live in.Your local county assessor’s office determines whether appraisers can count the square footage, finished or unfinished, as part of what’s known as the «gross living area.» 90003 90008 Walk-out basements and square footage 90009 90002 For the states that do allow listings to include a basement in the square footage of the overall living space, there must be an egress and ingress. 90003 90002 One reason for this rule is that you can not have a legal bedroom in a basement area without fire evacuation access separate from the rest of the house.90003 90002 If the above-ground floor is on fire, the room in the basement must provide at least window access to the outside. 90003 90002 This means a door you can walk out of to yard level on one side of the basement, says 90025 Sharon Chambers-Gordon 90026, 90025 90026 a real estate agent with Windermere Professional Partners in Gig Harbor, WA. 90003 90002 This is also known as a walk-out basement, and the square footage is calculated based on how much of the basement is above grade. 90003 90008 How square footage affects your mortgage 90009 90002 The overall square footage of real estate factors into an appraisal and, therefore, the financing of a house.Your appraiser must generally appraise the house for the sales price, or higher, in order for the lender to provide the funds. 90003 90002 Here’s what mortgage giant Fannie Mae has to say on the basement matter: «Only finished above-grade areas can be used in calculating and reporting of above-grade room count and square footage for the living space. Fannie Mae considers a level to be below grade if any portion of it is below grade, regardless of the quality of its finish or the window area of ​​any room.»90003 90008 How finished basement square footage affects your home value 90009 90002 Unlike commercial real estate, homes are generally not priced strictly on square footage. So whether a basement is included in square footage or not, a nicely finished basement generally adds to the value of a home, says 90025 Carrie Abfall 90026, a real estate agent with Re / Max Real Estate Professionals in Columbus, IN. 90003 90002 While the price per square foot for a swanky basement is not typically as high as main-level upgrades, an appraiser or potential buyer will certainly appraise the home’s value as higher with the additional living space of a basement.This is true whether the basement is a walk-out or below ground. 90003 90002 If the home with the finished basement wows a buyer, it may fetch a higher price, says real estate agent 90025 Randy Elgin 90026 with Keller Williams Realty in San Antonio, TX. 90003 90002 This is true even if the square footage is not included in the listing. Elgin advises that you offer what you think is reasonable, based on the home’s gross living area plus some fair amount for the unfinished or finished basement.90003 90002 Focus on the usable space and how much value you will gain from it. And include an appraisal contingency in the offer. That way, you can back out if the appraiser places a lower value on the home than you expected. 90003 .