As design and as built SAPS

[iMCaan]

I hope this thread is in the correct section.

 

Hi

 

The company that is doing our house as built SAPs as asked me to sign and return Part L1A 2013 Specification to sign off the dwelling, see attached. My concern is we didn't use as much insulation as stated on the form for walls (stated 100mm but used 50mm PIR) and floor (stated 150mm but used 100mm PIR for UFH). Therefore, the house won't achieve the stated u-values.
Any suggestions as to what to do? We are ready to move in.

Should I be concerned?

Oh boy this feels bad but I must ask, should I sign it as stated should I amended it then sign it? What are the consequences?

 

Thanks

 

[JohnMo]

Email them back and state what you did, they will update the U values etc.

 

Then if you get a fail, get ready to install solar PV to make up the difference.

[Mr Punter]

If you amend it the house will fail and you will need to spend ££££ on PV to get a pass.  That said, solar PV is quite useful.  It could still fail on fabric efficiency.

[iMCaan]

I was hoping you would just say just sign the form without amendments. How would they know what insulation you have used? 

arggggh I don't have the funds for the solar  After 5 years, we just want to move in. 

[JohnMo]

2 minutes ago, iMCaan said:

I was hoping you would just say just sign the form without amendments. How would they know what insulation you have used? 

arggggh I don't have the funds for the solar  After 5 years, we just want to move in. 

Then don't ask questions you don't want a truthful answer too - which isn't what you want hear!🫣

[iMCaan]

It's just frustration.

I asked the questions to hear the truth.

 

Besides solar, how long would you have to fit the solar?

Can they enforce adding insulated plasterboard, which would mean a lot of work?

 

Edited Wednesday at 12:39 by iMCaan

[saveasteading]

But have yph changed from 100 dritgerm to 50 pir? Much the same performance?

[iMCaan]

Yeh we used 50mm pir insulation in walls. The cavity walls were 300mm with in total (100mm blocks, 50mm PIR insulation, 50mm cavity and 100mm stone).

100mm PIR insulation on ground floor for UFH.

25mm PIR insulation for first floor UFH.

200mm earthwool between joists.

400mm earthwool above joists.

150mm PIR insulation for slopped roof.

 

[saveasteading]

That's not bad insulation. the first floor insulation is irrelevant too the rating.

 

600mm earthwool to roof? really? 

and 150mm PIR to the rest of the roof.

 

I dont have figures to hand but that might pass.

 

[Mr Punter]

1 hour ago, iMCaan said:

I was hoping you would just say just sign the form without amendments. How would they know what insulation you have used?

 

OK sign the form without amendments.  What you have in there is broadly the same as was specified.  Do you need to provide photos?

[iMCaan]

For clarity...We have two attic rooms. In the eaves (unusable space), it's 200mm earthwool in joists. The vertical and slopped wall of the attic rooms are 150mm PIR boards. There's some unusable space on top of the attic room ceiling and that has 400mm earthwool.

 

Within all cavity walls, it's EcoTherm 50mm PIR board insulation.

[iMCaan]

No, there's no mention of the photos in the email or on the form.

[ADLIan]

The SAP assessor will rerun the calculation with the revised insulation details. Hopefully all will be OK if some flexibility built into the design otherwise they should advise on options to get a pass (improved air test number?).

I don't think photo evidence was required under the old, 2013, version of Appr Doc L.

[iMCaan]

Thanks guys, let's see how heavy the punch would be. 

[SteamyTea]

Out of interest, who decided to change the specification, and for what reasons.

[iMCaan]

I don't think anyone intentionally decided to change the specification. Let's say it was my inexperience. I would have stuffed the house with insulation had I known what the SAPs were for.  I think we mainly followed the architect drawings instead, which stated the insulation required. I still added more insulation then what was stated on architect's drawings. I remember tradesmen saying why so much insulation. Luckily, adding more insulation as got the house spec. closer to the SAPs spec (I think). 

[kandgmitchell]

I think this unfortunately illustrates what had been wrong with the BC system for quite some time. Get a design SAP passed and then the specification gets changed during construction with often those changes not even mentioned at the end and an "as built" SAP comes out of the sausage machine. The latest changes have tried to tighten this up with photographs etc and more attention paid to what actually happened on site. It is however still catching people out because some builders just don't think it through. I designed and spec'd two houses that had high efficiency gas boilers for a client. His contractor changed these to electric boilers because the gas connection was going to take longer than the electrical one. Didn't need the gas connection at all now......No one asked if that would be OK. That caused a hell of a fuss upon completion I can tell you.

[Redbeard]

8 hours ago, iMCaan said:

I still added more insulation then what was stated on architect's drawings.

 

....and ended up with 50mm PIR (only, as far as I read) in the walls? Since SAP for new-build is a whole-house affair (with back-stop - worse - U values for each element if I recall correctly) unlike refurb, where it is 'walls must be x; roofs must be y' etc.) I am not saying 50mm PIR would not 'hack it' but it sounds like half or less what I'd have used. What was stated in the archo's dwgs? My U value calcs are only rough ('fag-packet' rather than software) but the lightweight blocks must be a lot better than the standard blocks in my default to get 0.25W/m2K. Was there really less than 50 PIR (say 100 rockwool) spec'd initially?

[saveasteading]

1 hour ago, kandgmitchell said:

wrong with the BC system for quite some time.

 

1 hour ago, kandgmitchell said:

No one asked if that would be OK.

 

It's not the BC system that failed here but the builder, as you say.

 

And if the builder causes a problem, however much it is unforeseen by them because of lack of knowledge, it should fall to them to resolve it. 

They have overstepped their ability.

Your design but they thought they knew better?

 

Or have I missed your point? what was the fault with the BC system?

[iMCaan]

See as design and as built images attached. It doesn't appear to be a big difference in u-values or is it?

[ADLIan]

SAP is not particularly sensitive to elemental U-values so hopefully OK - only your SAP assessor can give a definitive answer

[Nickfromwales]

On 29/01/2026 at 08:38, iMCaan said:

I think we mainly followed the architect drawings instead, which stated the insulation required. I still added more insulation then what was stated on architect's drawings.

As the principal designer, and I assume the author of your b regs drawings, they are responsible for the insulation being fit for purpose and sufficient for a “pass”. 
 

If their spec is under then it should fall back on them?

[iMCaan]

Hopefully, the as built spec. is sufficient. Will see by end of next week.

 

 

[Redbeard]

Re the sloping roof, unless they guessed it wrong 1st time (design U value), all other things being equal (which perhaps they are not*)I cannot fathom how they get a worse U value with 150 (as-built - apparently 0.2W/m2K))than with 125mm  (stated as 0.18). *Much closer rafter centres and fatter rafters (therefore larger timber fraction in the calc) in as-built than design?

On 28/01/2026 at 12:25, iMCaan said:

After 5 years, we just want to move in. 

 

So this is to the pre-2022 Regs, then?

 

 

[iMCaan]

Yes, we started ground work in 2021.