Latest spec for insulation for extension

Tim Robbins

Hi,

If you are getting an extension build, what is the standard spec for the insulation:

• for walls
• for ceiling of flat roof?

Is 100mm about right?

DOCARCH

All depends on 100mm of what?

(Min) u-value required for walls is 0.18 W/m2 K

(Min) u-value required for flat roof is 0.20 W/m2 K

To see what thickness of a specific insulation is required to achieve the required u-values you can look at manufacturers specifications/technical data, and/or, it's relatively easy to do simple u-value calculations (with online calculators).

muffler

Don't forget about your floors.

I'm relation to the walls do you plan on insulating the cavity or using internal or external insulation?

The flat roof would have various options and just like the rest of the structure there are a lot of variables.

Tim Robbins

Rang xtratherm this morning and was told for new builds, recommended U value for wall is 0.18.

And to achieve that with internal insulation you need an insulation board 110mm and your plasterboard of 12.5 so 122.5 in total thickness.

Was told 90mm insulation would get u value of 0.22. You wonder how much a difference of 0.04 makes?

muffler

https://www.boards.ie/discussion/comment/119443806#Comment_119443806

It's no different than driving within or over a speed limit. There's a set value that can't be exceeded otherwise it's in breach of statutory regulations.