Insulation advice wanted

[Lobster]

New project!

There's a small covered-over area outside the back door (4.8 m2), which I want to convert into living accomodation (ie extending the kitchen, basically.) It has an existing flat concrete slab for a roof, single-skin brick wall to the left and in front of the back door, and is open to the elements down the right side. Plan is to fill the right side by moving the back door and adding a window and some brickwork, then to bring it all up to habitable standard.

I'm doing this by the book which means a Building Notice, and I'm now trying to work out the specs needed for insulation to comply with the regs, which is where I'm coming a bit unstuck. I know I'll need lashings of the stuff in the roof, walls and floor, but how do I best work out the thicknesses? I've got bogged down with U values in Approved Doc Part L and am wondering if I'm going too far trying to take this back to first principles. Would John Q. Builder really do all that? Isn't it a case in practice of 'oh you need X mm of product A on the ceiling, Y mm of product B on the walls, etc?

Haven't been to see Building Control yet, but I'm assuming that they will expect to see and approve my proposals, rather than me expecting them to just give me all the answers?

Can anyone point me at an easy-to-follow source of info to guide me through all this?

Thanks David

[Set Square]

Well, it's the BCO who needs to be satisfied with what you're doing - so why not ask his advice on how best to achieve the desired result. In my experience they are usually very helpful if it is obvious that you are trying to do it right but are not quite sure what to do.

[Lobster]

Mm, take your point; it's just that I feel I should go and see him pre-armed with rather more info than I have now: therefore, "will it be OK if I do it like this" (and then an answer which he will hopefully build on) rather than "please tell me how to go about building this thing". I think he might just tell me to go and see an architect or something once he realises how far off I am at the moment!

David

[Mike]

Go to the Kingspan website (or get their booklet) and they show how much of their stuff is needed for each area to meet the regs. Even includes details of how much you can knock off for each of the many types of thermal blocks if these are used.

[Doctor Evil]

Best go over the regs so you don't need to heat it. Insulation is cheap and once built difficult to retrofit.

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[Rick]

There are some mistakes in obscure details for the IMM's of the world, but in breif

You need to get to 0.35 average, a smaller number is better. In cavity walls you put 100mm of fullfill rockwall (it must be the fullfill stuff not the normal stuff), or 50mm of kingspan, at many times the cost (kingspan is not fullfill)

In floors & celiongs 100mm of kingspan is loads, prefiably under or over rafter rather than between. The kingspan website has plenty of good pictures - go look at them.

Windows are the double glazed argon filled etc etc.

what you *REALLY* need to avoid is anything that runs from inside to out and conducts heat - but you can't avoid them all.

To work it out do this :-

Rockwall is 0.037 Celcon (B&Q) Blocks are 0.15 You get this number off the product)

blocks are 0.1 m thick, so you take 0.15 and mutiply by 10 - this is the R value you add this to the R value of the rockwall (100mm = 2.7)

now get you u value 1 / (sum of r values), in this case 2.96. This is not the exact U value of the wall, as you have wall ties in there which are old.

All I did was go for a much lower figure, 0.2 or below as an average accorss my whole building, adding extra in the easy places.

The BCO will check your insulation plans when he sees the DPC, if he don't ask him if your plans are OK.

The cheepest place to buy kingspan is B&Q (the big orange ones), even cheeper than seconds from seconds and co. Actually blocks, sand, cement and stuff is all cheep from B&Q - go to the trade desk, get trade prices, don't just pay the ticketed prices.

Rick

[Rick]

I would arge the "insulation is cheep" point, its more expenive than the other materials in my walls. In my roof (150mm of kingspan) its about the same price as real welsh slates .......

However given the cost of retrofit, and heating I have put piles in. Once sealed I'll see if the IMM theory of not neeeding heating works, before I splash out on heating.

Rick

[Lobster]

Is that 0.35 for the whole structure? How do you average out different components; eg if the ceiling and floor are way under, but the walls are over, how are they weighted?

Current roof is simply a 4-5" concrete slab. I can't find a comparable structure on the Kingspan site... presumably I need to interpose the Kingspan between the slab and a plasterboard ceiling, with an airgap above the Kingspan? And new ceiling joists between the Kingspan and the plasterboard? Sounds like a lot of depth, which is at a premium...

(Not in my single-skin brick wall there aren't!)

Thanks a lot, Rick. One key thing I want to do is work out what thickness of insulation I'll need to attach to the single-brick-thickness wall to keep BCO happy; cos if it's too thick the resulting room will be too small to make it worthwhile doing! Hopefully I can do the calcs now...

Cheers David