Extension - insulation very expensive!? alternatives?

[pixiepoo]

Hi

We have received our full plans back from the architect and we have endless amounts of Celotex needed.

They said:

70mm Celotex CG50000 cavity wall: 0.19 uvalue when finished

70mm Celotex FR5000 ground insulation: 0.20 uvalue

150mm Celotex FR5000 roof insulation and 40mm Celotex GD5040 under rafters: 0.13 uvalue

120mm Celotex FR5000 for ceiling and 60mm Celotex FR5000 for joists: 0.14 uvalue

A quote for this from our local builders merchant was over £5000 oh my gosh!!

Are there any alternatives that reach the same uvalues?? I have heard people mentioning getting seconds... do inspectors frown upon this?

Many thanks

 

[SimonH2]

Check out http://www.secondsandco.co.uk and also their shop on eBay.

Most of what they sell is the same as you'll pay several times more from at the builders merchant, but not quite dimensionally correct. I've been using some 90-100mm sheet to insulate the loft I'm boarding out - a fraction of the price of buying 1st grade (I bought one of their "pallet loads").

I can see three potential problems though.
1) As you point out, your BC inspector may frown on it, partly because :
2) It won't be exactly the thickness specified and :
3) It won't be the make/specific product specified.

You might need to speak to your architect to see if you can adjust the design slightly. For example, where he's specified 70mm, see if 70-80 is OK, or perhaps go up a size to compensate for the fact that you won't be using specific products but "some random product".

 

[tony1851]

Unless there is a specific reason (eg highly-glazed extension), the U-values quoted do seem onerous.
Walls are better with full-fill cavity batts, and they're a lot cheaper.
The roof spec also seems high - usually a total of around 125-150 thickness does the job.
But there may be specific reasons for the high spec - check with your designer.
(You can use seconds if necessary).

 

[pixiepoo]

Hmm, I will check with the designer, I know he subs the building regs work out to someone else. I must say I was a little surprised when I saw the spec! I am assuming building control won't request to amend them when they are checked? I'm not sure whether to phone them and ask what they would expect for our extension?

It is just a two storey extension on a cottage, it is large (6.5x5.5m) but only 7 cottage windows and a door. The roof insulation is nearly £2k on its own!!

 

[StevieV1]

Hi there

Im doing a double storey ext at the mo, similar dimensions overall to yours and I put 120mm Celotex in between rafters and 30mm under for roof. 80mm in walls including internal and ground floor ceiling and 80mm in the floor - cost about £2000. That was about 16 sheets of 120mm, 16 sheets of 30mm and 40 sheets of 80mm.

Try Building Materials Direct in Swindon.

Good luck

 

[pixiepoo]

Steviev1 thanks for your reply - I will definately go and check them out, thanks.

Can I ask - were those sizes given to you on your spec sheet from the architect or did you decide those based on the uvalues you needed?

The reason I ask is that if building control pass the plans that have been submitted (with the insulation sizes I quoted above) am I able to just change the depths to less when we build it, as long as I can prove that it still meets the minimum uvalue? Or will they expect me to follow the exactly and not pick and choose which brands we want to use?

 

[tony1851]

am I able to just change the depths to less when we build it, as long as I can prove that it still meets the minimum uvalue? Or will they expect me to follow the exactly and not pick and choose which brands we want to use?

Under building regs, you can make any changes you wish - including spec of insulation - as long as the changes you make still comply with the regs.

You are not required to stick rigidly to the plans, even if they have been formally approved.

 

[pixiepoo]

Hi tony1815

Just so I interpret this correctly, does that mean that say our spec says 0.19 for the roof insulation but the minimum standard is 0.22 (just for example) then when we come to do it we could actually do te minimum amount required, using whichever brand at a depth that is suitable for reaching that minimum?

I was assuming that BC would want us to use exactly what is on the spec but this makes me relax a little. This may sound a bit of a dumb question, but when they do their site visit how do they check your uvalues? Do they expect you to show them calculations of the product you've used?

Many thanks

 

[StevieV1]

Hi there

I am not a builder, just a keen amateur doing a self build.

Ive done a lot of working with the u value figures on the web and Celotex's website. Those figures quoted by your architect appear to me to exceed what you require - You dont need figures that low to pass building regs I would suggest.

What I did was looked at some council reference documents on the web which give all sorts of set ups for roof's, walls and floors and all the different insulations available and thickness of each to achieve minimum u values. I also used the calculator on Celotex's website as well to solve my insulation woes.

The 120mm for roof and the 80mm for the walls and floor is what my architect specc'd. My issue arose because I misread my plans and put the 120mm between the rafters i.e. under the roof creating a cold roof whereas the architect specc'd a warm roof i.e. insulation on top of the roof. The result of this being I raised my u value over what was permissible so had to find a solution to resolve. The solution was to add the 30mm under the rafters (so under the 120mm). I used the Celotex calculator to work this out and bought the extra 16 sheets of 30mm which cost about £250 so had it not been for this the insulation would have cost about £1750 ish.

Hope that helps

 

[StevieV1]

Ive just seen your comment about BC checking u values.

I dont know how they would actually measure it, but mine didnt. The BC officer came into the extension and said 'Theres Celotex everywhere!' in a tongue in cheek fashion and that was it.

Ive learnt that, well I suppose like everything in life, building is not an exact science! My BC have been pretty good, theyve come out at the various intervals and a quick look for about 30 seconds, had a quick chat and then gone. I must say its been pretty painless and good humoured.

 

[pixiepoo]

That does StevieV1 thanks.

I assume you mean something like this:

http://www.runnymede.gov.uk/portal/site/buildingcontrol/General_guidance_notes/

http://www.sedgemoor.gov.uk/index.aspx?articleid=6304

Was reading it last night and it was very easy to understand. My only concern is that they were updated a long time ago and wonder if they are still relevant?

 

[StevieV1]

Yes those are the documents I was looking at and worked to so I think they are up to date.

To get a definitive answer which is bang up to date, us the calculator on Celotex's website.

The supplier I suggested is the cheapest I could find. They advertise on Ebay as well, but you can do it over the phone direct. They take your order and then pass it to a supplier local to you who wants the job!

 

[StevieV1]

Try this as well:

http://www.google.co.uk/url?sa=t&rc...5qeqvrl7il1IQrg&bvm=bv.68445247,d.ZWU&cad=rja

 

[tony1851]

Hi tony1815

Just so I interpret this correctly, does that mean that say our spec says 0.19 for the roof insulation but the minimum standard is 0.22 (just for example) then when we come to do it we could actually do te minimum amount required, using whichever brand at a depth that is suitable for reaching that minimum?

I was assuming that BC would want us to use exactly what is on the spec but this makes me relax a little. This may sound a bit of a dumb question, but when they do their site visit how do they check your uvalues? Do they expect you to show them calculations of the product you've used?

Many thanks

Relax! As long as you keep to the minimum U-values quoted in the 2010 edition of Approved Doc. L2b, you will be fine, regardless of what it states on the approved plans.

 

[theoldun]

Sorry, but who ever done your U values do not know what they are talking about.
Assume this an extension under L1B and not a new build under L1A.
Firstly the 5000 range has been recently introduced by Celotex with a K value of 0.21W/mK as against the 4000 range of 0.22W/mK. Basically this makes very little difference with regard to the resulting R values and U values except for being more expensive.
Cavity walls first, your target U value should be.0.28W/m2K, however R and U value is determined more by K value of your internal block work then the insulation. If you know what block work you are using then we will advise, how ever we never use a partial fill, as it means working from back to front. We use a full fill cavity with Dritherm 32
Ground floor target value is 0.22 W/m2 K. Insulation value is determined by perimeter area ratio and as we do not know these an average of 0,5 will require 70mm of Celotex GA4000 and 25mm ditto as up stand.
The U values and what you have wrote for roof and ceiling joist is from another planet, and make no sense what so ever.
Is roof pitched or flat?
Is it single storey extension or double storey?
As Manchester Tony has said providing you are working to L1B and you meet the target values, do what you ecking well like.
Regards oldun