U values for extension-help!

[Jason C]

Hi

I am building a 250 sq foot extension to the back of my house (South Facing) and would like to know if I am under or over cooking the insulation. The details are:-

Windows:- A rated, double glazed argon gas filled with u value 1.28

Walls:- Cavity wall build with 160 mm ecobeed insulation. (I think this gives a U value of 2.2 from what I have read?)

Roof windows:- 4 x Velux 78x98 with U value of 1.3

The existing house (3 bed semi D) was built in 1991. A few years back I converted the attic into a bedroom and insulated accordingly. The front of the house which is noth facing tends to be colder and I plan to try to insulate these with warm board or pump ecobead in once I figure out is it cavity wall or cavity block build.

I am eagar to try and make sure that I get a decent insulation level in the extension and considering that the entire back of the extension which is 5 meters in lenght will be glass I am wondering should I go for tripple glazing with a U value of 0.8? People are telling me that tripple glazing is not required on windows which are south facing?

Any help would be great

J

 

[onq]

Refer the matter to a BER consultant for a definitive comment - you could do this as part of acquiring a BER cert for the property, which lasts for 10 years should you decide to sell or rent.
Further to what Superman has posted below, you would ask the assessor to comment on the entire house, not just the extension.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.

 

[hastalavista]

Could be wrong here but is the rating of windows not a trade process and not independently done.

re the 160 cavity, have u an engineer on board, AFAIK anything beyond 100 requires sign off and special ties

01/09/2011 ps it seems from next post the upper limit is 150 [but more ties are required for 150]

 

[Superman]

triple glazing is less necessary on south facing. You will need to check the cost against the improvement.
Your ecobead sounds like it would be .22 not 2.2.
Hastalavista: I believe that Homebond are ok on anything up to 150mm, above that requires engineer's special design.

It would be a good idea to look at the overall u-value for the house - there isn't too much point in sticking an amazing but expensively insulated extension if all of the heat loss is through the rest of the house. So also look to improve draughts, efficient boiler, any obvious locations for insulation etc. in the existing.

Generally, your specification is pretty good. Without more information, I suspect that the triple glazing may be unnecessary - given that the heat loss is likely to be through the rest of the house. If it can be done for a low extra cost, then go ahead.

Getting an actual BER done by somebody competent will give you a lot more information to play with.

Don't forget the grants available.

 

[Jason C]

Thanks a million.

I probably will stick to the spec above. The ecobead is 150mm on inspection so sounds like it will be ok. I will check with the builder that appropriate ties are used.

 

[onq]

On a matter of structural compliance, you are best advised to check with an engineer.

Building professionals have feedback loops where they inspect premises built by others.

My experience of builders is that their feedback loops tend to be limited to events on a job

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.