Friday, October 14, 2011

Frost heaving and cold bridge fixing in foundation wall

Last fall we got a new big sliding door to our garden deck. During the winter we had problems opening it, probably due to frost heaving. Our carpenter suggested we should insulate the outside of the concrete slab that the house is built upon. This concrete is also a nasty cold bridge into the house floor. So I got the spade out and started to dig.

The concrete slab is about 50 cm ( 2 feet) deep, at least around the perimeter. I also removed the lower plank to make sure to expose all of the concrete.

Today it is common to add 5 cm ( 2 in) of styrofoam insulation to the foundation wall, so I decided....

...5+5 cm should be good. I think it is a good idea to add as much insulation as possible while at it. I managed to cover all the exposed concrete.

Then there is an issue of leading any water away. So I added some fabric, "Leca balls" and a drainage pipe.

Close it up.

I also added 60cm of 5 cm thick styrofoam from the wall and out. This will also help to insulte, and will later be hidden under the new deck that will reach all the way to the sliding door. All set for the winter! When it gets real cold, it will be interesting to compare inside floor temerature close to this wall  to similar positions close to walls with no foundation wall insulation.
Update: It turned out that the problem with the sliding door was the upper wood above the sliding door that twisted during the winter. Some additional screws have now solved that problem.

Summary in Norwegian: Vi har installert en stor skyvedør mot hagen i vårt rekkehus fra 1978. Forige vinter begynte den å gå treigt, antagelig på grunn av telehiv. Dermed gikk jeg i gang med drenering og isolering av betongplaten som hele huset står på. Hensikten er å unngå at det blir frost under denne, og å fikse den enorme kuldebroen det er å ha sementgulvet i stua koblet rett ut i kuldegradene utenfor. Isolasjon er ikke noe man skal spare på, det er bare å kline til med det det er plass til. Her ble det 10cm mot veggen og  5cm plate 60 cm ut fra veggen. Til sommeren kommer vår nye hage platting her oppå isolasjonen i bildet. Andre steder i hagen planlegger jeg å få hvertfall de 10cm mot muren. Gleder meg til å se hvor varmt gulvet blir der hvor det er ekstra utvendig isolasjon i forhold til der hvor det ikke er. 


Anonymous said...

This is a great idea. I was just wondering. My house has an old basement wall that is about 1,7 meters deep, and the newer half of the house, where the basement is about as deep as yours. If I isolate the way you did around the newer part, would need to dig up all the way to the bottom of the wall on the old part too?
One of my major problems also is drainage. Water enters in to the old basement and the humidity is an issue. I am using dehumidifiers now and was planning a full drainage. Would the kind of drainage that you did there be enough do you think, or would I need to dig 2 meters down and use gravel in the more traditional way?

Svein* said...

The wall exposed to the outside air will have the greatest heat loss. Any insulation here will be most important. The further down you can dig, the better you will insulate the overall wall. In general you should put the drainage below the point where you want the wall to be dry. Use drainage pipe at the bottom and make sure to enclose the gravel with a cloth so the soil will not enter into the gravel. I think a full drainage is the only way that is sure to work.

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