Wall built with foundation blocks. Insulation requirements?

[RonnyRaygun]

As it says in the subject line really.

My plans have been ignored and an extension has been built with 300mm foundation blocks instead of a double skin cavity wall as specified.

How much Kingspan (or similar) will be required internally to comply with current building regs?

 

[theoldun]

What make of blocks Ron?
3.6 or 7.3N?
Do you know the lambda, or R of blocks?

What you looking to achieve? 0.28W/m2K?

I do know the lambda of celcon insulated foundation block.
3.6 are 0.25W/mK.
7.3 are 0.32W/mK.

Let me know and will sort you out. You old boy's tis the word
Regards oldun

 

[^woody^]

55mm celotex

 

[RonnyRaygun]

Just went to have a look, but couldn't find any evidence Let's assume they are 3.6N, as it's a single storey foundation and 7.3 would not be necessary.

Having spoke to the builder he has informed me that 300mm foundation blocks give satisfactory insulation by themselves. If this is true, it makes me wonder why they aren't used more often...

Just done a fag packet calc based on lambda of 0.25. Gives a U-value of around 0.83
215mm blocks with a lambda of 0.15 give a U-value of 0.87.

So two things: Nowhere near compliant, and 85mm of space wasted as a 215 block would have done the job just as well.

I think around 60mm of Kingspan is required to comply?

Please correct me if wrong.

Doing this job as a favour for the next door neighbours. Went round earlier for a chat and did a little inspection.

Drawings have been almost completely ignored. Some things aren't a problem, some are...

Apart from being built with foundation blocks...
Roof is around 150mm too low
Soffit sticks out twice as far as on drawings
Wrong tiles. Builder reckons they comply with 16 degree pitch but have my doubts. Client doesn't like them anyway...
DPC not lapped with existing
Facing bricks used below DPC (under door opening). Very doubtful frost resistant.
Floor not yet laid so DPM not lapped with DPC. I may be wrong but I would have done this before building walls.

What do you think Old Un?

 

[RonnyRaygun]

55mm celotex

Well done again Woody. A more accurate calc, and I make it 52.5mm, so I'll give you that one!

 

[^woody^]

Stop referring to that person as a "builder"

 

[RonnyRaygun]

Stop referring to that person as a "builder"

Wasn't calling him a builder last night I can assure you!

Oh, he's also put in a flat ceiling where the ceiling should be vaulted.

Luckily he's only got as far on the roof as putting the timber in place. I've left a message telling him to take it down and do it again properly.
Not much we can do now about the walls other than use the correct thickness of insulation.

 

[noseall]

Sounds like an idiot to me.

 

[maltaron]

It seems that many so called builders cant read drawings. The one I used on my extension (chosen by recommendation) cound'n't. Luckily I employed him on labour only and project managed myself. I would suggest that if your extension is not built to the drawings then the BC will not pass it.

 

[RonnyRaygun]

It seems that many so called builders cant read drawings. The one I used on my extension (chosen by recommendation) cound'n't.

This job has been subbed out by a builder who was recommended to the client by their own daughter! I'm not overly impressed with either of them, as it was the main contractor who I spoke to last night, and who insisted that the foundation blocks were compliant without insulation, and that the tiles were compliant. He says it was agreed with the building inspector...maybe to use foundation blocks, I very much doubt they agreed that no insulation was required.

The whole reason I told my neighbours to get the plans approved, rather than work on a building notice was so that the plans could be followed without issue.
I'm a structural engineer and building regs drawings are not my day job so wanted to ensure any issues were picked up before the work started. I would however have liked to have been consulted before they deviated from the plans.

I would suggest that if your extension is not built to the drawings then the BC will not pass it.

Yes, I would have thought that BC would be keen to see approved plans followed, although as long as it complies with regs I guess they aren't too bothered. It's not their job to ensure the aesthetics etc are correct to the drawings.

 

[^woody^]

There is no requirement to follow the approved plans, but any deviation must comply to the required regulations. All that happens is that the BCO may or may not ask for new drawings to show the altered work

 

[RonnyRaygun]

Just had a heated conversation with the main contractor.
He has assured me that 300mm foundation blocks are accepted by Three Rivers DC without insulation. I told him that I find that very unlikely, but am going to call BC later to find out.

After I listed all the areas where the drawings hadn't been followed, he told me it is OK because the BI has passed it He suggested I was accusing him of not knowing what he was doing, and he could take me round to countless jobs where customers are satisfied. I stopped short of telling him that I think he does know what he's doing, but is deliberately being lazy and doing it on the cheap.

Most of this has no effect personally on me, but the roof detail does. We agreed to share the party wall, and the roof being 6 inches lower really messes up the junction between my extension and theirs. This is why I took time to get the levels correct.

 

[theoldun]

Ron,
Internal and external resistance = R 0.18
20mm Render C = 0.5, R = 0.04
300mm block C = 0.25 R = 1.20
55mm Celotex C = 0.022 R = 2.50
12.5 plasterboard and skim C = 0.14 R = 0.11
Total R = 4.03 = U value 24.81.. We cover ourselves on cold bridging by 10%. Therefore U value = 28W/m2K

Use celotex PL4000. Sounds like your builder is performing well and appears to be a first class chap, just lacking supervision.

Tell him to drop your plate height if not right, or show him the hole in the hedge.

See woody has been gazing down at his golden nuggets again.
Regards oldun

 

[RonnyRaygun]

Ron,
Internal and external resistance = R 0.18
20mm Render C = 0.5, R = 0.04
300mm block C = 0.25 R = 1.20
55mm Celotex C = 0.022 R = 2.50
12.5 plasterboard and skim C = 0.14 R = 0.11
Total R = 4.03 = U value 24.81.. We cover ourselves on cold bridging by 10%. Therefore U value = 28W/m2K

Thanks Old Un. That's what I thought.

However, would you believe it, I spoke to the Chief BCO this afternoon. He looked through the file and found a note apparently saying "300mm aerated blocks to be used without insulation". I argued that even the best Turbos would not comply without insulation, and he suggested that the BCO must've been of the opinion that it would be no worse than existing because it's very small. When I said it was 18 square metres he said "not that small then".

Sounds like your builder is performing well and appears to be a first class chap, just lacking supervision.

Yeah, if I wasn't at work all day I would be supervising! When I asked him why he hasn't followed the drawings he told me it was because he didn't think I would have any more involvement and didn't think anyone would care...says it all really.
I'm annoyed as I think my neighbours are getting ripped off in order for the builder to increase his profits, as he priced to my drawings.
They are an elderly couple and will just agree with anything the builder tells them for an easy life.