Home foundation trends in 2020 are encouraging for sustainability as slab on grade wins

It's slab on grade foundations for the win!

The NAHB study showed that 65% of new single-family home starts in 2020 were built on slab on grade foundations, 22% of homes were built with a full or partial basement and 12% with a crawl space.This means that more people are choosing a slab on grade instead of a basement, with the share of new homes built on slabs steadily increasing from 46.0% in 2000 to 65% in 2020, while the amount of new homes built with basements dropped from 36.8% to 22%.

Why do we think this is good news? Well, basements and crawlspaces certainly have some place in home construction, but there are countless benefits to slab on grade construction that go overlooked simply because we are creatures of habit. For no reason other than familiarity, people will often assume a home ‘needs’ a basement or crawlspace in certain circumstances, or that there is some great value to subterranean life.

In urban cores where there are height restrictions and setbacks from neighboring homes, it can for sure be of value to take advantage of the added space. However, in areas with a bit more breathing room where homes are being built on larger lots, there are countless reasons to forgo a basement in favor of a slab on grade foundation, remembering that in colder climates, frost-protected slab on grade foundations are tried and true even into the far north.

A basement uses dirt as insulation, where a slab uses 'insulation' as insulation, so they both work fine as long as you put the right amount of insulation (or dirt) for the climate where you are buiding. Read more here aboutthe benefits of a slab on grade instead of a basement foundation.

More from the NAHB home foundation study

New homes built on slab on grade foundations are most common in the South Central west region where 95.7% of homes are started that way.In the South Atlantic 79.4% of homes are built on slabs, 67.7% in the Pacific region, and 48.1% in mountain divisions. Slabs are most popular in the West South Central division of the US where new single-family houses have been primarily constructed on slab-on-grade foundations over the last ten years.

A warmer climate makes building on slab more cost-effective compared to full or partial basements. Slab foundations also need the least amount of maintenance over the lifespan of a home. In the East South Central division, 43% of new homes started in 2020 were constructed with a crawl space and 38.0% were built on slabs.

美国各地的基金会类型也存在很大的地区差异。在较冷地区，建筑规范通常要求地基必须建在霜冻线以下的住宅，主要都有全部或部分地下室。新房中全部或部分地下室比例最高的地区是新英格兰，79.8%的房屋是这样开始的，其次是中西部地区(77.2%)，大西洋中部地区(69.5%)和东部中部地区(54.3%)，房屋的地下室地基低于等级。

In these regions, full or partial basement foundations offer additional finished floor areas at a marginal increase of construction cost over traditional frost walls. Although as we mentioned above, if you have enough land, a frost protected shallow foundation - which is an insulated slab on grade with an additional insulated skirt - may actually save money as it reduces the labor and the excavation required.

The average area of finished basement was 1,156 sq. ft. in the East North Central division, 998 sq. ft. in the West North Central division, 921 sq. ft. in the Middle Atlantic, and 734 sq. ft. in New England. Nationwide, the average finished floor space of basements was 1,137 sq. ft. in 2020.

Ecohome slab on grade homes

We have constructed several demonstration homes over the years that have achieved LEED Platinum certification, and all were built onslab on grade foundations.We noticed in this report that slabs are less popular in colder climates, and we do hope to see that change as it makes better financial sense to build on insulatedfrost protected shallow foundations而不是霜墙或地下室，不仅是为了前期建设成本，还为了节省耐用性和维护费用。

All the demonstration homes we have built are in very cold climates, and all are extremely energy efficient, very comfortable, and built at a comparable and even lower cost compared to code built homes. To find outwhich areas may be susceptible to frost heave in foundations and need frost walls, see here.

用平板建造的房屋通常更经济，更耐用，给你带来更健康的室内空气质量。你不需要用泥土包裹房子来防止它翻倒，你也不需要住在地下。平板住宅不一定对每个人都理想，但如果它看起来很吸引人，不要让你自己被一个只喜欢建造地下室的总承包商说服，并向你灌输偏见的信息。

除了成本、耐用性和健康的住宅，石板的另一个好处是更好的生活质量。如果你能住在地上，为什么要住在洞里?在寒冷的气候中，你看不到太多的阳光，让阳光从一扇朝南的大窗户射进来比从地基顶部的小窗户射进来更有益。

Why not to build on a crawlspace

And as for houses built on crawlspaces, we’d like to see that number drop to close to zero.地面上的平板直接放在地面上，而另一方面，爬行空间，就是你可以爬行进去的空间。为了帮助你决定哪一个更好，首先花一个下午去洞穴探险，这样你就可以问自己，你是否真的喜欢在一个充满虫子的黑暗地方爬来爬去，同时用你的头撞东西。如果答案是肯定的，那么爬行空间就是为您准备的!

Read more here abouthow to fix and insulate a crawl spaceand you will learn a lot about why we dislike them so much - and read herewhy we feel that a slab on grade is a much better choice than a crawlspace.

Problems to avoid in code built basements

由于新浇筑的混凝土地基需要5年时间才能完全干燥，所以许多地基会发霉也就不足为奇了。This is one of the multiple reasons why we don't recommend them,即使已采取措施，以确保其完全保护每一个表面的防水膜进入地面水分。

Concrete is like a sponge, and when left unprotected from moisture, it will continue to wick moisture from the ground and distribute it into your home for as long as your home stands.

All that ground moisture will be continually sucked into the concrete and will then often cause fungus and mold issues in your batt insulation, framed wall and drywall. This is especially true as many building codes require a vapor barrier on basement walls, which does nothing good but only contains moisture so walls begin to rot. If you have amoldy basement, find out here how to solve it- and if you are building a new basement - make sure to do it the best way possible by reading our guide onhow to insulate a new basement to avoid mold, here.

Preventing mold in basements

The solution to this one is really quite simple - if we stop building below grade with walls that were designed for above grade, basements wouldn't smell like old gym socks and spread mold spores throughout your house.

如果空间限制意味着你的新家有一个地下室，你不能等5年它干了才完工，要求你的建筑商不要使用标准的6 mil聚蒸汽屏障。Instead choose asmart membrane that can breatheorEPS rigid foam insulation with a built in vapor barrier- or evenuse vapor retardant latex paint.We do not recommend is using spray foam in basements, for all the reasons here. The definitiveguide for how to build new basements that can dry out properly and avoid mold is here.

Preventing flooding in basements

Spring flooding of basements is very common and most times can be easily avoided.Why basements flood in the first place is pretty easy to answer – it’s a hole in the ground and the ground is wet! Basements are sometimes below the water table to begin with, but water tables rise during the spring snow melt, and without proper perimeter drainage you could have a big problem as water finds it's way in. Forthe definitive guide on why basements flood and how to stop basements flooding, see here.

Preventing radon gas in basements and crawlspaces

Radon gas was not high on the radar of builders and home owners over the last few decades,but as it is the second leading cause of lung cancer after smoking in the USA & Canada, it is quickly becoming a household term.

Many newer homes will have radon barriers and vents pre-installed, and if building a home with a crawlspace or basement, the questions remain:

• Which areas of the USA are most at risk from radon gas?
• 哪些是家庭氡气体最好的测试?
• How to deal with high levels of radon in existing homes with no mitigation system in place?

Thankfully Ecohome has guides and products for all those by following the links above, but again - a slab on grade or insulated frost protected shallow foundation will prevent most cases of radon gas entering the home in the first place - making it a better choice for foundations as well as being more sustainable.

Where possible use lower carbon concrete for building foundations, slabs and basements

Building foundations, crawlspaces and basements all involve using concrete, which has an extremely high carbon footprint with cement production accounting for 7% of global carbon emissions.人们认为，这个问题正在加剧，而此时我们本应减少碳排放，以防止失控的气候危机。

For many years, environmentalists have encouraged city planners, architects and construction professionals to find alternatives to concrete in the quest for a lower carbon footprint in the built environment.

In the quest forzero carbon homes, a Canadian company may have found the solution with a carbon-sequestering concrete system that appears to have the attributes ideal for general use across all building sectors, and that is gaining fans in the green building community. Find outmore about lower carbon concrete here and see if it is available in your area at the same cost as regular concrete.

If using CMU blocks to build frost walls or a basement in the North Eastern USA or Canada, you can alsomake a choice to buy carbon negative CMU blocks - find out more here.

Bottom line - properly built slab on grade foundations make more sense...

If you are still not yet convinced of the benefits of a slab on grade or a frost protected shallow foundation instead of a basement or crawl space, please let us know why in the comments section and we will be happy to discuss!

Now you know more aboutthe benefits of choosing a slab on grade foundation. Learn more aboutbest practices for energy efficient and durable basement construction and renovationsin these pages: How to build a slab on grade foundation - technical guide How to build a slab on grade on standard soils How to build a slab on grade on problem soils Building better basements: how to insulate your basement properly Crawl space insulation tips for insulating crawlspaces properly Find more about green home constructionin the EcohomeGreen Building Guide pages- also, learn more aboutthe benefits of a free Ecohome Network Membership here.