Saturday, January 1, 2011

Insulate inside walls step by step

Our wodden house from 1978 has only 10cm (4") insulation. This winter I decided to add an additional 10 cm of insulation to the inside of the wall while upgrading our home movie theater in our living room. I wanted to hide all electrical and video/audio wires. I did some research on how to do this correctly, while keeping a tight vapor barrier. Here is how I did it, step by step. 

 This is a section of the original wall where there is also a window. I started by removing the winow trim and cutting away 10 cm of our wooden floor to give room for the new wall.

With all the dry wall removed you can see the old 0.15 mm thick plastic vapor barrier. It should be placed on the warm side of the wall. In Norway that is the inside of the wall. It is, however, ok to have a maximum of 1/4 of the wall insulation on the inside of the vapor barrier.

Since the original insulation was in the vertical direction, I added the next 5 cm in the horisontal direction. Then I added the new vapor barrier which was taped together with the old one. Any holes found was fixed with some duct tape. I also useed silicon around adjacent walls. It is very satisfaying to have a completely tight barrier.

Here is where you see the advantage of having the inner most 5cm of insualtion inside of the vapor barrier. All electrical wires, can be hidden here without any worries of punctuate the barrier and getting condensing problems in the wall. The inner most 5 cm insulation was in the vertical direction.

Insulation on the inside completed, a full 20 cm in total for the wall. Some of the dry wall in place. To the very left you can see a hole for a speaker cable.

There it is. The completed wall with the first layer of paint.
You can find more technical details on vapor barriers here: Vapor Barrier explained


Joshary Jones said...

Great thing you decided to insulate your house more. A well-insulated house saves money and energy. It will also keep comfortable in all seasons.

swiss said...

Hello Svein,

thank you for your good posting. Images tell more than words.
Thank you for your energy to share "energy saving action plans".

If I searched "inside insulation" or german "Innenraum Dämmung" the most websites and information I found are concerns and discribtions of problems, when to insulate the walls from inside.
Most mentioned problems are dampness and thermal bridges.

What are your longterm experiences with that "problems"?

It seems to me that this insulation you present could be done by a layman?


We live in the south of germany and for some reasons it is not possible to insulate it (we live in the first floor ~100m2); ground+first floor and build out roof) from outside.

1) I thought all the time, it would be better to use material, that is vapor proof in itself (e.g. polystyrene 5-10cm). You use some kind of wool to insulate.

2) But I find it not a smooth solution to end with a wooden plane... (why not to end with polystyrene - clear you can damage it very easy - but how often would this be the case...).

3) What I also encounter difficult is the wall around the window. There is nearly no place to put insulation there (in our case).

4) Do you think it is possible, if the heating and water pipes are in the insulated wall, that these pipes could freeze (e.g. walls ~50cm and two weeks -25°C)?

a emotional good time wishes

Svein* said...

Hi Michael,

I have seen no problems, and do not expect any either. I would say a layman can do this better than a professional since he can spend more time checking the details. By adding insulation first horisontal and then vertical there will be almost no thermal bridges (except around the windows. Making sure the vapor proof plastic is sealed completely in all ends and corners is important.

You could use polystyrene to make it vapor proof, but I think there might be some issues with fire safety. If you use it , it should be covered with something that do not burn easily.

Windows can be difficult. Try to be creative, and see if you find a way of making thermal bridges as small as possibe.

In Norway you are not allowed to have water pipes in the outside walls. If your wall has an even insulation you can make a linear estimation from inside and outside temperature if the water will freeze. If it is +25C inside and -25C outside your pipes will be fine if they are not more than half way into the wall.

Enrich John said...

I was pinning away for such type of blogs, thanks for posting this for audits