Introduction: Stop Outside Air Blowing Under Walls in Old House

About: Here I am!

The Issue:

I bought an old house where when the wind blows you can feel a draft come across the floor and chill the rooms. In the summer this wasn't too much of an issue as it's not extremely hot here, but now that its cold the house has become a bit hard to heat.

Summary of this project:

I needed a way to stop this influx and subsequent leaking of air that wouldn't visibly damage any trim or my newly refinished wood floors.


In the diagram above I have shown cause of the issue, "Air Gap / Blowing Air" that is able to pass from the outside, past the sill plate, into the interior wall and out of the gaps in the trim around the floors outlined in light blue.

  1. The way of solving this was to carefully remove the 1 inch quarter round trim from the 8 inch trim board / floor.
  2. Next I carefully drilled 3/8 inch holes through the seam between the 8 inch trim board and floor where it wouldn't be visible once the 1 inch quarter round trim was replaced outlined above in yellow. Be very careful not drill through the wall studs or any pipes / electrical wires that may be in your walls! - You only need the hollow spaces.
  3. I used the "Professional" Great Stuff* Foam spray sealant to fill in the Air Gap (Purple in diagram). Starting in one of the middle holes, spray enough to start seeing the foam come through the neighboring holes to the one you are filling then proceed to the next hole, until all of the holes have been filled.
  4. Keep in mind this foam expands to a few times the size of what is sprayed in as a liquid. It will create "worms" or tubes of foam that will protrude out of the drilled holes. Be careful not to overfill as these can touch the finished floor or trim.

Step 1:

**Shown above are tubes of foam that have protruded out of the drilled holes.

5. You will want to allow the foam to dry completely, at lease 2 hours, before any cleanup work is to be done.

Step 2:

6. After the foam has dried thoroughly, cut the excess foam away from the trim board and floor with a hack saw blade.Use the blade only without the saw handleto allow the blade to flex and be able to saw as closely as possible to the seam between the trim board and floor.

* If you have some excess foam stuck to the floor where it would be visible, use Acetone (nail polish remover) to clean it off. Allow the acetone to dissolve the foam and wipe up gently with a soft cloth to avoid damaging the finish.

Step 3:

7. I wanted to keep my 1 Inch trim from "floating" after it had been nailed down so I applied a thin bead of Silicone II to the seam before nailing them down.

Step 4:

* Since I reused the old 1 Inch trim I ended up with the same old (visual) gaps between the Floor, 1 Inch trim and 8 Inch trim. This is why I used Silicone II in the previous step, over time the nails will loosen, but the silicone will keep the issue from being exacerbated.

8. After the silicone II is dry, you can add wood putty to the cracks and stain the putty as shown above.

Wood Putty is Easy!

  1. With your finger take a small amount of wood putty and make a ball about the side of a raisin.
  2. Push the small ball into the gap and smear it as far as it will fill the gap.
  3. Continue the above until the gap is filled with putty.
  4. To shape the putty and make a clean fill pattern use a damp rag and gently wipe the newly puttied gap.
  5. Clean up any excess with water and a clean rag.

Staining Wood Putty is Easy!

  1. Simply brush on the stain of your choice and allow to dry for 5~10 minutes depending upon the darkness you are looking for in your stain.
  2. Wipe off excess with a clean dry rag being sure to rotate often.
  3. Experiment with the above until you reach the desired stain color.

Step 5:

Now that you have stopped the air gap, and had the air gap in the first place, it is possible that you do not have any insulation in your walls. Check your walls for insulation and if possible use a blown-in insulation to fill the hollow space in your walls for maximum efficiency. It is also possible that you do have insulation in your walls but the air was blowing under the bottom of it, I had it both ways in this house.

9. Blown-in insulation if necessary.

This has been a tremendous help to efficiently warming my home and not feeling a breeze when indoors. My propane bill has also fallen off significantly after completing this around all of my trim and baseboards. Hope this has been helpful and will allow some of you to be a little warmer this winter.