Insulated raft for fully glazed extension

[Huckleberrys]

Hello

 

I am in the process of designing a fully glazed extension and was hoping to use an insulated raft...does anyone have any idea how this would work with floor to cieling full height glazing?I can't exactly sit the windows on the I solution upstand!

[JohnMo]

3 minutes ago, Huckleberrys said:

designing a fully glazed extension

Daft question, how does a fully glazed extension get anywhere near building regs, min insulation values?

[Huckleberrys]

Roof won't be glazed, just 3 sides...you can get some pretty decent u values on windows these days!

[Huckleberrys]

And planners are stipulating it needs to be fully glazed...believe me I'd rather it wasn't!

[kandgmitchell]

Well get ready to follow paragraph 10.10 of Approved Document L1 because you will not comply with 10.7(d).....

 

Extension of a dwelling
10.7 When a dwelling is extended, elements should satisfy all of the following.
a. New thermal elements should meet the standards in Table 4.2 and paragraph 4.7.
b. Replacement thermal elements should meet the standards in Table 4.2 and paragraph 4.8.
c. New windows, roof windows, rooflights and doors should meet the standards in Table 4.2.
d. The total area of windows, roof windows, rooflights and doors in extensions should not exceed
the sum of the following.
i. 25% of the floor area of the extension.
ii. The total area of any windows and doors which no longer exist or are no longer exposed
due to the extension.
e. Existing fabric elements that will become thermal elements should meet the limiting standards
in Table 4.3 by following the guidance in paragraphs 11.2 to 11.4.
10.8 When a dwelling is extended, any fixed building services or on-site electricity generation that are
provided or extended should comply with the guidance in Sections 5 and 6.
10.9 As an alternative approach to paragraph 10.7, the area-weighted U-value of all thermal elements in
the extension should be shown to not exceed the area-weighted U-value of an extension of the
same size and shape that complies with paragraph 10.7.
The area-weighted U-value is given by the following expression.
[(U1 × A1) + (U2 × A2) + (U3 × A3) + …]
(A1 + A2 + A3 + …)
Where:
U1 = the U-value of element type 1
A1 = the area of element type 1
and so on.
10.10 As an alternative approach to paragraphs 10.7 or 10.9, the Standard Assessment Procedure may be
used to show that the dwelling primary energy rate, the dwelling emission rate and the dwelling
fabric energy efficiency rate for the dwelling and proposed extension do not exceed those for the
dwelling plus a notional extension. The notional extension should be the same size and shape as
the proposed extension and comply with paragraph 10.7. The openings in the notional extension
should conform with paragraph 10.7d, with the door area set as equal to the door area of the
proposed extension and the remainder of the openings being classified as windows.
NOTE: Where the performance of elements of the existing dwelling is unknown, data in the
Standard Assessment Procedure Appendix S should be used to estimate the performance.

[JohnMo]

So glazed is ok, so long as the rest of the house is improved, quite a bit. (Para 10.10)

[kandgmitchell]

This works best on an older house where the new works in effect reflect an improvement despite the windows. On a much newer house it gets harder to justify.

[Huckleberrys]

It is an extension as part of a complete barn conversion. Only 2 windows in the place currently! And the rest of the barn will have very low u values with a timber frame built internally.

[SteamyTea]

May be worth asking our top notch glazing expert @craig how it is done.

[saveasteading]

On 19/10/2023 at 18:03, Huckleberrys said:

planners are stipulating it needs to be fully glazed...believe me I'd rather it wasn't!

The roof needs some support, so if you allow solid corners and abutments to the existing, and a kerb/ upstand are you getting anywhere near the permitted area? 25% of  floor (internal or external).

I know it won't look so flash but that's philistine Engineers for you.

To maintain the glazed look you can clad the structural bits in aluminium or glass.

[Huckleberrys]

I was thinking of going for a steel frame, with external supports. The amount of glazing part is not the issue, that is fine. It's just if it's possible and the detail of doing it with an insulated raft. It's only 3x5m the extension.

[saveasteading]

8 minutes ago, Huckleberrys said:

detail of doing it with an insulated raft. It's only 3x5m the extension

OK. We've been distracted.

My own preference is that extensions have similar footings to the existing. That limits differential movement.

 

What do you mean by a raft please? I have seen several different interpretations on BH.

And why does it appeal? 

Then you will get my thoughts.

But yes you can use a raft.

On 19/10/2023 at 16:37, Huckleberrys said:

I can't exactly sit the windows on the I solution upstand!

I don't know what you mean.

[IanR]

On 19/10/2023 at 15:37, Huckleberrys said:

I am in the process of designing a fully glazed extension and was hoping to use an insulated raft...does anyone have any idea how this would work with floor to cieling full height glazing?I 

 

54 minutes ago, Huckleberrys said:

It is an extension as part of a complete barn conversion.

 

20 minutes ago, Huckleberrys said:

It's just if it's possible and the detail of doing it with an insulated raft. It's only 3x5m the extension.

 

Are you using an insulated raft for the rest of the conversion. If not then it seems a lot of trouble to go to for a 3m x 5m area, when your glass "walls" aren't likely to be better than 0.5W/m²K U value.

Are you thinking frameless glass? If it's framed the detailing should be too difficult. Have you got a link to the glazing you are considering, or a section?

[Huckleberrys]

For the rest of the barn I was thinking of basically making a raft with pir...no worries about it bursting or anything due to it being enclosed in 2ft thick granite walls, but thought for the extension maybe best to use a proper product with built in upstand. 

 

I wasn't thinking frameless...although as narrown a sight line as possible.

[Huckleberrys]

I meant "insulation upstand" not "i solution"...fat fingers sorry.

[ToughButterCup]

38 minutes ago, IanR said:

? If it's framed the detailing should be too difficult.

Shouldn't? 

[Adrian Walker]

On 19/10/2023 at 15:37, Huckleberrys said:

Hello

 

I am in the process of designing a fully glazed extension and was hoping to use an insulated raft...does anyone have any idea how this would work with floor to cieling full height glazing?I can't exactly sit the windows on the I solution upstand!

 

Did a job some time ago with floor-to-ceiling patio doors.  Used solid foamed glass under the frame - https://www.foamglas.com/en-gb/products/

[IanR]

35 minutes ago, ToughButterCup said:

1 hour ago, IanR said:

If it's framed the detailing should be too difficult. 

 

Shouldn't? 

 

Doh!  yep it "shouldn't" be too difficult.

Edited October 20, 2023 by IanR

[craig]

3 hours ago, SteamyTea said:

May be worth asking our top notch glazing expert @craig how it is done.

You’d think eh 😂

 

What’s wrong with designing in some compac foam and sit your windows/doors on that, should be fine to do that.

 

 

[saveasteading]

2 hours ago, Huckleberrys said:

the rest of the barn I was thinking of basically making a raft with pir.

So do that, with the concrete all the way to the edge. Then you can sit anything on it. Probably a simple slab for the barn, but perhaps a case for a structural raft at the extension, but it is secondary.

[Huckleberrys]

9 hours ago, craig said:

You’d think eh 😂

 

What’s wrong with designing in some compac foam and sit your windows/doors on that, should be fine to do that.

 

 

I think this is the way...forgot about this stuff whilst I was thinking about it all. Thanks for input everyone.