Department of Environment study of actual U-Value performance of walls and roofs plus my any thoughts on ensuring my walls don't have the same issues

[AliG]

I just came across this, it was posted on the other forum 5 years ago.

 

Very interesting report on actual performance of walls and roofs versus specified performance. Many discrepancies although most of the largest discrepancies were due to outrageously bad workmanship such as not putting any insulation in or putting it in after the wall was completed.

 

I notice they mention a sheltered housing project that was specified with 40mm of PUR but built with 20mm of EPS. When they examined the wall they also found there were no wall ties. Perhaps it was built by the same people who built PFI schools in Scotland.

 

http://projects.bre.co.uk/uvalues/U-values.pdf

 

I was looking at it as my walls are about to go up. They are partial fill with 100mm of Celotex. Plus 37.5mm insulated plasterboard on the inside. They will build the internal leaf first which should make installation of the Celotex in the cavity easier. I was trying to think if there was anything I could do to ensure it performs as expected other than telling them to be tidy and make sure it is hard against the inner leaf. I was thinking of taping the joints, but as there will be no ventilation into the cavity I don't really see wind washing being a big issue. The outside face will be rendered and the inside face will have a parge coat so air tightness should be pretty good. As the walls are Porotherm which has only 1mm of mortar and a much lower tolerance in block sizes (+/- 0.5mm) it should be easier to fit the Celotex neatly and tightly to the blockwork.

[IanR]

 

"Real World" performance is nowhere near that declared to the Regulator!

 

If it ever happened in Automotive there would be a scandal. 

[gravelld]

16 hours ago, AliG said:

I was thinking of taping the joints, but as there will be no ventilation into the cavity I don't really see wind washing being a big issue. The outside face will be rendered and the inside face will have a parge coat so air tightness should be pretty good. As the walls are Porotherm which has only 1mm of mortar and a much lower tolerance in block sizes (+/- 0.5mm) it should be easier to fit the Celotex neatly and tightly to the blockwork.

Still too much opportunity for air ingress imo - top and bottom, cracks appearing over time with movement, what sort of joists do you have? If normal joists: shrinkage. I don't believe there's a cavity in the land which is air tight. Personally I am still not convinced about rigid blocks as an approach, but if I was forced into it (space considerations) I'd foam and tape them.

Edited October 14, 2016 by gravelld

[AliG]

The upper floors are suspended concrete so no joists. I assume they are mortared onto the blockwork and the large coat also goes across the joint, but I will be checking!

 

I was up asking the supervisor about the insulation this morning. He said that it is held pretty tight by the ties. I think I will see how it starts to go up and then see if they need to do any more than their standard job. At least there is no hiding it if they build the inner leaf first.

[gravelld]

That's right. I'm not sure a "standard job" is good enough really, if he means the standard most trades get away with.

[Brickie]

One issue you could look at would be the positions of any extractors & possibly building short pieces of 100mm drainage so the insulation can be cut snugly around them. 

If you don't,when the plumber comes to core drill the extractors from inside to out-bye bye insulation in those areas. 

[Brickie]

Re the grid showing on IR-given the OP is using 100mm insulation perhaps two skins of 50mm insulation,half lapped horizontally & vertically would reduce this significantly? Some straight jointing is still going to be unavoidable,but massively reduced a la brickwork water bond. 

[AliG]

I am using the CW4100 boards. The blocks are 100x300x224 plus 1mm mortar. So on a straight wall the 1200x450 CW4100 should fit exactly with no cutting.

 

Tongue and groove insulation sounds interesting, I hadn't seen any. Now I am looking, it appears that  Xtratherm make it, will have a look.

 

Originally we had just plasterboard on the inside, but changed to insulated plasterboard. Although the insulation is only 25mm, at least it means there will be some insulation overlap.

 

Edited October 16, 2016 by AliG

[AliG]

I am having a look now, it may actually be too late as I have a funny feeling the main contractor ordered up the insulation last week, he certainIy ordered the blocks.

 

I don't think overlapping would be practical as the sheets are made to match the blockwork lines and be held in place by the wall ties.

 

Maybe taping the joints is the thing with the best benefit to cost. I notice that Kingspan recommend taping on some of their very high performance insulation, but not the PIR.

 

I am also looking at the heat loss calculator. It suggests that the walls only account for only around 13% of the heatloss as designed. Even if the U-Value ended up being 0.2 rather than the 0.15 calculated it only adds around 4% to heating costs.

Edited October 16, 2016 by AliG

[Declan52]

Just use pir cavity wall insulation as its all tongue and groove and comes in a variety of different widths. All the cavity wall insulation we use in NI is all t&g. Don't think we ever done a house using rockwool batts.

[AliG]

Thanks Declan. I am using PIR. The main PIR suppliers on the mainland are probably Kingspan and Celotex. Their products are straight edged, not T&G. Having looked for it, the Xtratherm may be hard to come by, no where near as many people sell it, I wonder if they have a higher market share in NI.

 

I am having the same issue with the roof insulation where I may have to get it shipped over from NI.

[PeterW]

47 minutes ago, AliG said:

Having looked for it, the Xtratherm may be hard to come by, no where near as many people sell it, I wonder if they have a higher market share in NI.

 

 

 

Thats odd as the big Xtratherm factory is at Chesterfield. 

 

Have you tried Buildbase as they are a stockist

[Declan52]

Kingspan would be the rolls Royce over here but as its the most expensive it's not wide spread although as I got a great deal I used it on mine. 

Xtratherm would be considerably cheaper so is more wide spread here. They are based in the rep of Ireland but have offices in eng. I bought all my floor and roof insulation from them direct as it was a large order so maybe if you are ordering enough to fill an artic lorry they might be able to ship it from Eire if they can't source it from their English plant.

[AliG]

I'll ask my contractor on Monday. Thanks for the help guys

 

[TerryE]

This is one where you need to keep a very close eye on how well the contractor is placing and fixing the insulation. Any looseness or gaps can allow front to back convection within the cavity and this can halve the effectiveness of the insulation.  The devil is very much in the detail here, and not something that many UK builders are known for, at least in things that they don't view as material -- like thermal performance.