Minimum Wall Thickness

[dcherowbrier]

Hi All,

Desperately tried to google an answer to this but I have failed miserably.

I am building a small side return kitchen extension. So small that every inch really matters. So I'm trying to keep the external wall as thin as possible.

Due to the size of the extension I believe I fall under the following:

1.13 For small extensions to dwellings (for example, ground-floor extension to single rooms such as kitchen extensions in terraced houses, porches where the new heated space created has a floor area of not more than about 6 m2), reasonable provision would be to use construction details that are no worse in energy performance terms than those in the existing building.

Given the rest of the house is 9 inch solid brick walls I have a lot of scope.

So, just how think can I go and it still be an actual wall? I had a few thoughts in my head:

- 4 inch timber frame filled with 100mm celotex insulation and some sort of external board with render on the outside
- 50mm thermal breezeblock with 50mm external insulation
- 100mm thermal block with an external render

Each of these gives a 100mm wall, if there's a design where I can get away with thiner though...

Any advice would be appreciated.

Dan

 

[^woody^]

You need to consider keeping damp out, condensation prevention, fixing units and services, windows, and structural support of the roof with your 100mm wall ideas.

 

[dcherowbrier]

You need to consider keeping damp out, condensation prevention, fixing units and services, windows, and structural support of the roof with your 100mm wall ideas.

The thermalite 100mm blocks claim to meet the building regs for water penetration. It has no windows or services but a small timber frame roof. Would the condensation be caused by the wall being too cold? With a thermalite block it'd still have a better u value than solid brick so I'd hope not?

 

[^woody^]

Thermalite blocks are designed for use in a cavity wall, so the qualities mentioned relate to that use. Any masonry wall of only 100mm thickness will be prone to condensation issues, and it has nothing to do with u-values. You will need a membrane for damp prevention and also some insulation to remove the cold internal surface.

And the inspector may not accept a single skin wall supporting a roof.