Recommended insulation for new-build cavity wall?

[M2006]

What's the recommended insulation for a new-build cavity wall? Last time I used fibre-glass bats from Wickes, but I've just spoken to a builder who says he doesn't like using them because, if they get wet, they can hold mold spores that are bad for health. Instead he recommends foil-backed Kingspan which he says is much more expensive and hard to get cheap/at a discount.

Is what he says true but unnecessary or is he just talking the price up? If the fibreglass is getting wet, you've surely got other problems to worry about.

[Phil L]

Fibreglass dries out just fine, even if it's dripping wet when installed...it *shouldn't* get wet after. IME he's taking the p!$$ and he's probably got a load of the foil backed stuff off the back of a lorry or he's over-ordered on a previous job and he's trying to get shut of it.

[dg]

He's talking rubbish. I would question his other knowledge about building too.

The fact is, good working practice and the manufacturers guidelines dictate that the bats are kept dry in storage and the wall is kept dry (ie the top of it covered) while being built. The bats should never get wet.

The insulation contains a water repelant to deal with the slight bit of moisture which may soak through the outer skin. It does not allow mould growth, and even if it did just how are spores supposed to move around in a full fill cavity and then get into the inside room through the inner wall?

Rockwool and fibreglass insulation bats quilt are fully certified by the BBA and are in common use.

He wants to charge you =A350 a sheet and buy it off ebay for =A325.

dg

[Staffbull]

My extension 5 X 4 m HAD to use 50mm kingspan throughout clipped to the wall ties using clips, there was no alternative!! also 65mm kingspan under the floor !! buying it from your builders merchant will be much cheaper, especilly if you go and open an account as with an extension youll need a fair bit of stuff :-)

[dg]

There are lots of alternatives.

Isowool, Celcon 'Turbo' blocks, bigger cavity, thernal boarded etc etc.

In building, there is never just one solution.

dg

[sm_jamieson]

How do you mean, you HAD to use 50mm kingspan. Who told you ? The building control officer ? Were you in a particularly exposed area, where full fill batts are not considered to resist water penetration enough ? Did you use thermal blocks inside ? I'm always curious when someones says they HAD to do something. Cheers, Simon.

[The Natural Philosopher]

If he only had 50mm to play with, kingspan is the only thing that insulates well enough to be street legal to latest regs.

They let ME get away with 100mm of rockwool in a timber framed house though.

[Staffbull]

In the specs for plans, asked BCO and he said use kingspan, would have preferred a cheaper alternative but no. two walls are concrete block, and no were not in an exposed area, also kingspan had to be used in the floor, jablite was not possible ( polystyrene) roof had to be done in Tyvek too !!! the most expensive !! and welsh slate, which I dont mind as its the best! but it's funny that I can get spanish or Chinese slates for half the cost from thousnads of miles away for half the price of Welsh and i'm only 25 miles from the Quarry!!

[dg]

Thats the trouble when a designer takes the easy option and does not consider the actual costs to build.

There are similar products to tyvek, but half the price. Jablite can often be used in the floor, but just needs a thicker sheet. Use a better block and can save on the insulation. Have better glass or argon fill.

Also, it may be possible to have less insulation in the extension, but compensate elsewhere - like increase loft insulation or upgrade the boiler

dg

[sm_jamieson]

When I did my plans, I found some examples and they all used 75mm cavity and full fill batts. All the extensions round my area that are being done use the same. I didnt like the idea of using aircrete blocks inside, but soon realised its best to spec the plans how its "usually" done. I guess the BCO had his reasons. However the BCO cannot refuse an identical product of a different brand if it performs the same. The BCO is not a designer ! If he was insisting on Welsh slate, it sounds like the there must have been some listed building type situation. Maybe he was having a laugh ... Simon.

[Staffbull]

I think it is standard practice on Anglesey to roof with Welsh slate if it goes through building regs, ALL grant roofing has to be Welsh slate, but then again it does put money back into the local economy

[Andrew Gabriel]

I did a bricklaying course earlier in the year, and it was stated there that all cavities would now have to be kingspan or equivalent. Fibreglass batts would no longer meet new regs.

I've still seen fibreglass batts being used since, but I've also read the BRE (?IIRC) report that almost no new houses are actually meeting building regs Part L anymore.

[salesguy]

Where did you do the course - that information is completely wrong. New Part L is much more complex than the last one, and the options are almost endless. Key issues are the type of heating system (gas = good, electric = bad!) and floor area, window area etc etc.

Fibreglass batts can still be used to comply in full fill or partial fill dependent on cavity width.

Info here

may be of use - and certainly more accurate than your lecturer who must be on commission!

SalesGuy

[Tony Bryer]

EST report into compliance with the 2002 AD

other findings: "Up to 3 low energy lamp fittings had been specified in the original proposals for the dwellings in the sample. The fittings had generally been installed in hallways, landings and some bedrooms, but few remained in the completed and occupied dwellings. Most had been removed by the occupants, and occupants expressed their intention to replace soon those few that remained."