The Gap Between Foundation And Framing: How To Mix It


You’re done with your house’s interior and exterior structuring, you’ve installed the roof, and are about to begin painting the outside when you spot something that almost makes your heart leap out of your chest. There is a GAP between your foundation and the frame of the building. What, why, and how, you ask? You’ve come to the right place, my friend.

A gap between your house’s foundation and frame forms because of a thin insulation membrane known as a sill seal. To serve as an air seal against the elements, this membrane occupies the space between the bottom of the frame and the top of the foundation. This then results in the formation of a gap.

While this may seem like a disaster, and an early blow to the image of your young home, it is not much to fret about (depending on how bad it is, of course). Below are some of the causes of this gap, as well as some possible solutions. Let’s get right to it.

Why Is There A Gap Between The Foundation And The Framing?

There are quite a few reasons behind the unsightly gap. In most situations, the (inexperienced) homeowner has nothing to worry about. This gap is known as a cove joint, and it is perfectly normal. 

When the concrete that will serve as a house’s foundation is poured, it must be left to set and harden for at least 48 hours (depending on the environment, weather, etc) before the wall frames are put in place. 

The wall concrete is then poured into a groove known as a key way to keep it in line with the foundation and it too is left to set for 48-60 hours. During this time, the walls cure and contract, just a little. When the floor concrete is poured, it too will cure and contract into itself. With time, a gap (or cove joint) will form as the walls and floor inch away from each other until they are dry.

Another reason why a gap might form between your house’s frame and the foundation is one that we have all been taught to avoid since kindergarten: rush jobs. Builders, homeowners, and home inspectors often find themselves (and each other) in a Mexican standoff over this very issue, yet no one ever seems to learn. 

This would be fine and dandy if time-outs were the only penalty to fear. Unfortunately, your money is what’s at stake here, as well as your time. Workers who perform rush jobs actually consume more time because of all the re-doing that will be required.

One of the things that both builders and owners tend to rush through the most is the foundation itself. Whether it’s mixing, pouring, or setting the concrete, a significant number of so-called “experts” often find themselves erring. 

Mixing concrete is not as simple as one might think, so great care must be taken. Make sure the person(s) responsible for mixing sticks to the correct instructions. 

However, the setting of the concrete may be the most critical stage of laying the foundation. It is recommended that you give concrete a window of about 48-60 hours to dry and harden. 

You can also (carefully) play it by feel to determine whether the concrete is ready to bear weight. Avoid working on wet concrete whenever possible.

If you start erecting the wall before the concrete dries properly, you will be increasing the likelihood of a gap appearing. As the foundation sets, it contracts into itself ever-so-slightly. Were a wall to be erected on this foundation, the two would slowly move apart from each other until the concrete is finally dry.

For wooden wall frames, a gap is the result of a thin membrane that is placed between the bottom of the frame and the top of the concrete foundation. This thin polyethylene foam membrane is a standard air sealing solution for most American homes. Sill seals also feature ribbed surfaces that are well suited to keeping unwanted air and vermin out of your home.

A gap between the foundation and the frame can also emerge if the concrete runs unevenly, another stroke of a rush job.

How To Fix The Gap Between Foundation And Framing

While the gap serves a purpose (where wood framing is concerned, at least), it is still not the prettiest thing to look at. As such, one might feel the need to explore ways to cover this gap.

One of the best ways to do this is to make use of caulk. I would recommend that you use it for the interior of the home, where it is much less likely to be at the mercy of the elements. A quality caulk will stick to the wood and concrete like glue, completely erasing the joint. The caulking will also enable you to even out some of the lopsided concrete.

The exterior is a slightly different story, however. Because of direct exposure to elements like rain and heat, caulk may not be the best solution, although manufacturers continually try to make improvements in this arena. Instead, go for all-weather-proof adhesive tape, such as 3M’s All Weather Flashing Tape. One important thing I forgot to mention is the application of primer paint before sticking adhesives to a gap. The primer will help protect the tape from elemental damage and prolong its aesthetic appearance.

Best Gap-fillers

We have briefly touched on some of the tools used to fix this gap. These items are not hard to find. Check out your local hardware shop or head to Amazon for some interesting solutions to your problem.

The elemental all-weather tape is just so useful, and it is no surprise that people have turned to it to address this DIY issue. One of the best iterations available today is the Ulti Flashing Tape from Barricade. 

Made from highly durable rubber, this flashing tape is everything you need and more, where repairing the foundation-frame gap is concerned. You have nothing to fear from the elements thanks to the tape’s incredible staying power. 

The Ulti Flashing Tape is water-resistant and will remain adhesive in temperatures of 0-150oF. It also has an impressive tensile strength of 60lbs/ inch.

The other gap sealer we discussed is the caulk. There are many impostors out there today, looking to take advantage of newbie DIYers or those who aren’t in the know where caulk is involved. One of the trustworthy brands in this arena is DAP, which has unveiled one of the caulks you can buy today. Introducing the Kwik Seal Adhesive Caulk.

At 5.5 ounces, I must admit that this is hardly enough to cover substantial gaps and openings. However, the Kwik Seal caulk makes up for this with incredible adhesiveness and adaptability. 

Feel free to paint over it if you wish because nothing will happen to this watertight seal. The caulk can also stick to a surface in temperature ranges of about -20-150oF, another nod to this filler’s never say die attitude. 

DAP has also gone to the great lengths to combat mildew and mold. The use of cured caulk is one of the said lengths that has yielded results for Kwik Seal. The ultimate (and odorless) filler for indoor foundation-frame gaps.

Other notable caulks include Gorilla Glue’s Paintable Silicone Sealant Caulk (which is also mold and mildew-resistant) and Red Devil’s Duraguard Kitchen & Bath Siliconized Caulk (which can also be painted to match any desired color). 

Why Should I Fill The Gap Between The Foundation And The Frame?

There are a few reasons why one would want to fill this gap permanently, especially on the interior side. If you are like me, the first of these would undoubtedly be vanity. 

That little gap is rather unsightly and gives a home an air of incompleteness. Applying a caulk or appropriately colored strips of flashing will go a long way towards rectifying this. Skirting boards would also be a neat way to conceal the gap or any indiscreet caulk or tape.

The second reason is to protect the gap and, by extension, your home from the elements. Excessive rain can (and often does) lead to issues such as seepage, where water seeps into your house through this gap. If unchecked, this could lead to foul smells in and around the house, as well as mold and mildew. If this goes on for long enough, the wooden frame might start decaying and cost you even more to replace. 

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