U Values and quantities of glass

browfish · 1 Oct 2010

I am in the process of finalising plans for our extension before submitting them.
we had planned an extension that is only about 2m deep but all along the back of the house approx 15m long. THs was going to be glazed almost the full lenght, full height with 2 sets of sliding doors.

Reading up a little more tonight i have noticed that you are not usually permitted more than 25% of the new floor area in glazing. Being only 2m deep this means that the glazing is more than 100% of the new floor area. I know i can subtract the existing windows which are to be lost/unexposed. I also understand that i can improve other thermal elements of the existing building to allow additional glass but i need a good calculator for this. Does anyone know of a good free one?

At the same time we will be modifying the roof with 2 new dormas to creat in effect a second floor. DOes this count as an extension with extra floor space as this can offset some of the glazing? If it counts as an extension can it be combined with the rear extension or is it to be treated separatley?
thanks in advance for any guidance

freddiemercurystwin · 1 Oct 2010

Just employ a SAP engineer to provide the calcs for you. It would be cheaper than buying the software probably. I do not know anyone without the proper software who can do SAP calcs. Have you ever seen the results of a SAP calc? They're about 8 pages long!

jeds · 2 Oct 2010

You can download free SAP software from Complete Picture. It will allow you to do your own calcs etc. and is a full program completely free to use. If you want reports for building regs though you will have to subscribe. As it happens Complete Picture is very reasonable (at £85 per year) compared to £700...odd from the likes of Elmhurst and others.

Strictly speaking BC shouldn't accept your reports unless you are qualified. But there's a good chance they will.

freddiemercurystwin · 2 Oct 2010

I stand corrected!

browfish · 2 Oct 2010

thanks for that. I will download that now.
Any input on whether the roof alteration/converstion counts as an extension and can this floor space be included when calculating the 25% of glazing?

Any idea on how to work out the construction of your walls and floors without cutting a great big hole through them? It is a 1930's bungalow so god knows how it was put up.

DevilDamo · 3 Oct 2010

How about assume worst case, i.e. 9" brick?

Credo · 15 Oct 2013

I notice that you are building a bungalow extension 2 x 15 mainly glass. Did you get it thru SAP tests? Is that the size and design, mainly glass that you decided on?

browfish said:
thanks for that. I will download that now.
Any input on whether the roof alteration/converstion counts as an extension and can this floor space be included when calculating the 25% of glazing?

Any idea on how to work out the construction of your walls and floors without cutting a great big hole through them? It is a 1930's bungalow so god knows how it was put up.

browfish · 15 Oct 2013

Never actually went with that design.
In my experience they never actuall ask for a calculation so could probably have done it. This is the third house i have done and wasted so much money on different calculations from insulation to structural etc that building control wernt interested in.

Credo · 15 Oct 2013

browfish said:
Never actually went with that design.
In my experience they never actuall ask for a calculation so could probably have done it. This is the third house i have done and wasted so much money on different calculations from insulation to structural etc that building control wernt interested in.

Thank you.

DevilDamo · 15 Oct 2013

Credo said:
I notice that you are building a bungalow extension 2 x 15 mainly glass. Did you get it thru SAP tests? Is that the size and design, mainly glass that you decided on?

Nothing like bringing up a thread over three years old

Credo · 15 Oct 2013

DOHdesigns said:
Credo said:

I notice that you are building a bungalow extension 2 x 15 mainly glass. Did you get it thru SAP tests? Is that the size and design, mainly glass that you decided on?

Click to expand...

Nothing like bringing up a thread over three years old

Best thing to do when you are considering doing the same thing. Browfish kindly replied. Have a good day one and all

DevilDamo · 15 Oct 2013

They replied but it didn't answer your question as the OP never went through with that particular design. If you are looking at going above the glazing threshold, then assume you will be asked for a calculation by BC that will either prove the new openings over the existing are not a lot worse or a SAP calculation. You would be expected to pay approx. £200 for the latter.

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U Values and quantities of glass

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