U-value balance for whole house

[brian]

Hello, 
I'm going building a house in the South West of Ireland with the fabric first approach.
I have purchased PHPP and trying to DIY it.
Is it Ok to have more Insulation in Floor and Roof than the walls?
Floor = 0.108
Walls = 0.15
Roof = 0.117

Or should the U-value's be more even?

[nod]

While the U value is important 

Its easy to get obsessed with numbers 

Whilst ours isnt passive we achieved a good U value A large very warm and cheap to heat house All done DIY Worth twice the build cost Including the land 

purchase 

I think it’s important that you finish up with a home that suits your needs and budget 

and also looks good 

 

[A_L]

hello and welcome,

 

Your U-values are fine, though I would try and reduce the wall value if possible. The reason to keep U-values similar is principally to prevent condensation on the higher value areas but this is on a much higher  difference, e.g. the latest Scottish regs ask for walls averaging 0.22 but allow local areas of 0.7.

[Declan52]

The walls usually have the least with the roof the highest. It's much easier to lay 300-400mm of loft insulation but if you put that much in a cavity then it can cause many more issues like much longer wall ties, closing the cavity etc. 

As long as it's total is good is the main objective. Don't forget any window or door you put in no matter how high tech it is will still be at least 3/4 times as high a u value as your wall. 

[joth]

While you definitely want to get it all right first time, remember the floor is hardest to upgrade later so if it's a cost tradeoff, don't cut corners on the floor installation

[SteamyTea]

Isolate each element, then calculate losses for each against the expected temperature ranges they experience.

Pay special attention to windows and doors, corners and joints, and the often forgotten effects of air movement.

Then remember that if all your insulation is open to external air, this can reduce the effective values.

When you come to build, unless you are very conscientious, any hidden holes will loose energy. But as our chancellor said "not going to tell you where they are, but you have had 3 years knowing that they are there somewhere".

Ok, not what he actually said, but you get the idea.

 

[brian]

Thanks for all your reply, It sounds like I'm on the right track.