insulating a garage: one last question

[Stephen]

Hello,

I asked a few weeks ago about insulating garage and the consensus seemed to be that I need to fix 8x4 sheets of kingspan or similar to the wall between wooden battens. Then I have to fit plywood 12 or 18 mm onto the battens to protect the insulation from knocks and to allow me to fit shelves, cupboards, etc.

A local builders merchant sells polystyrene much cheaper than kingspan. I realise that it is a poorer insulator but if I had a suitable depth would it work well? Does anyone know the u-value of

75mm or 100mm polystyrene? I can't ask the manufacturer because I don't know who makes it, polystyrene seems to be sold generically. Is polystyrene a fire risk though?

Last question: If the insulation is 8'x4' and the plywood is 8'x4', how can I fit the plywood onto battens to the side of the sheets of insulation? Do I cut a couple of inches from the insulation? Do I really want to cut bits off and throw it away when it costs so much! Or do I put the insulation vertically and board horizontally?

Thanks, Stephen.

[george (dicegeorge)]

i think polystyrene is much more flammable and gives off poisonous gases are you going to be welding etc in the garage?

[g]

[george (dicegeorge)]

kingspan seconds are much cheaper,

google kingspan seconds

sometimes the ends are malformed or broken..

Stephen wrote:

[The Natural Philosopher]

its about 1/2 the insulant and is a real fire risk. Burns fiercely and gives off toxic fumes.

Not recommended, but its your life..

If you want CHEAP use 4" deep studs and rockwool. 6" is better, but 4" is portty good.

You should stud at 2 ft intervals, and cut the foam to fit. Then tape over the studwork with metal foil tape before boarding up. Do any electrical first fix then as well.

So 4x2 studs for rockwool, and use noggins to stop it slumping, and you may want to use something like tape to hold it in place before boarding up, or 2x2 suds and 50mm celotex taped up with foil tape ..

[John Rumm]

k value of the PIR foam boards is about 0.021 to 0.025, and polystyrene is about 0.035 to 0.040. So for 50mm of the stuff you get best case u values of 0.42 for PIR and 0.7 for the polystyrene. That means you need about 85mm of poly to match 50mm of PIR.

polystyrene a fire risk though?

If you get the stuff designed for building applications then it ought to be treated with a flame retardant.

Personally I would use the PIR foam and dispense with the battens altogether apart from around doors and window openings etc where you need them for aesthetics and holding the board edges.

I did my workshop not long ago, and used PIR foam boards, gave them a squirt of expanding foam to tack them in place, and then screwed through the ply and foam into the wall using long (5.25") screws into brown wall plugs. Using a long Bosch multimaterial 7mm bit, its very quick to drill straight through all the layers in one hit, and then just tap the plug and screw through the hole. Six screws per sheet seem more than adequate for fixing - even if the boards are taking shelves. For the large heavy shelves, I used long metal spur type struts, fixed right through the cladding into the wall again.

[Tim S]

Stephen coughed up some electrons that declared:

Try googling for Jablite U-values - sure that will turn up something.

Jablite et-al is treated with a fire retardant. For a shed it's OK, as it is under a concrete floor (well under the screed). Still gives of noxious fumes in a fire though.

PIR is better in that respect. By the time it gives off fumes, you'll probably be toast anyway (higher temps needed).

I just bought 50mm Ballytherm 8x4' sheets for 14+VAT each. That gives you an idea of how much you might be able to get it for, 2nd grade (ie dinted but perfectly useable).

Where are you? I know a supplier who does runs to mid Kent and East Sussex...

Cheers

Tim

[Jules]

Can't you buy it pre-cut into more suitable strips? Here the framework's typically built to a small number of standard spacings (usually 16" or 24") using 2x4's, and insulation sold pre-cut to exactly the right width to fit between them.

The framework's normally either 8' or 10' tall here, but advice is to attach any board with the longest side horizontally to add extra strength, even though that's typically sold in 8x5' sheets here (so there's a temptation to just put it vertically when the long side matches the wall height). Try to stagger the sheets so that you don't end up with a seam all the way up the wall at any point. Start at the bottom and work your way up, so you're not buggering about trying to attach a 'full' sheet at the top of the wall :-)

cheers

Jules

[The Natural Philosopher]

No. It isn't. Its designed to go in SCREEDS. Strangely, these seldom catch fire.:-)

[Tim S]

The Natural Philosopher coughed up some electrons that declared:

And the stuff that's designed to go in lofts? (Wickes have some)

Cheers

Tim

[John Rumm]

Panto season already?

Oh yes it is:

"Jablite board is available in sheet form, size 2400 x 1200mm and in thickness ? 25,40,50,60,75 and 100mm.

It is EPS 70 as defined in BS EN13163 and classified Class E containing a flame retardant additive."

[Stephen]

Thanks. I read your post before but I missed the part about not having battens. That would save a lot of work. So you only used one screw in each corner and one either side, halfway up?

Did you use 50mm board? Would it work with deeper boards and deeper screws or is that best avoided?

I think I will try and find some seconds of kingspan because that would give me more insulation per unit thickness, if the price difference is not too great. It would avoid any uncertainty about the safety of polystyrene too.

Thanks again.

[Dave Starling]

the 8x4 50mm sheets are sub =A320inc vat new from your local builders merchants. If you buy at least 5 you should be able to negotiate free delivery.

Dave

[John Rumm]

It not only saves work (and timber - hence money) it also removes the thermal bridge the timber introduces.

I actually fixed a little in from the edges / corners - so the screws ended up roughly equidistant from each other, rather than side by side at the ply edges. All you really need it to hold the ply an insulation flat against the wall.

I used 50mm foil faced board, and 1/2" ply. You could use thicker board, although the screws get expensive when you go much over 5.5" (I used

5.25" 12 gauge twinthreads - that seemed to pull the boards in nice and tight with a couple of inches in a brown plug in the masonry.

Where in the UK are you? There is a supplier in Essex that will do 50mm at £12-£14/sheet...

Indeed, and you can get away with 2/3rds the thickness as well.

[Stephen]

Thanks again. I will get round to doing as toy suggest and screw the plywood through the foam to the wall, avoiding the cost and hassle and heat losses through the timber frame.

I will try to get some kingspan seconds rather than use polystyrene. Did you also line the roof with the same?

Are you happy with the results or is it worth considering the 75mm sheets?

Thanks again.

[John Rumm]

In the workshop I did - just under the rafters. The existing roof had soffit ventilation so I did not need to worry about that. Headroom was a non issue - so rather than mess about with insulation between the rafters I just stuck 50mm under them. I did not bother boarding the ceiling, and just screwed through some strips of ply ripped of the end of a board to act as giant washers. 4 screws per sheet with a couple of ply strips was adequate to hold it all in place. Finally went round with a foam gun and filled any gaps.

I think 50 will be more than adequate. It seemed cool enough in there today in spit of the heat. The real test will be in the depths of winter, but I can't see it being too difficult to keep it warm enough to stop tools rusting etc.

[stan]

On Jul 1, 10:02=A0pm, John Rumm wrote: Don't know about a stand alone garage but in many jurisdictions and always within a residence or garage attached to a residence, any kind of foam/polystyrene insulation 'must' be covered by one hour fire resistant material; namely that is nowadays usually half inch plasterboard. Any kind of attic or air space above ceiling roof insulation must be ventilated; IIRC there must be 3 sq. feet of venting per 1000 sq. feet of area and it must allow 'cross ventilation'. Also vapour barrier. Some types of foam are vapour barriers; other types require the installation of a plastic vapour barrier on the warm side of the insulation. In typical construction that is usually just behind the the wall panelling/plasterboard. A relative has just installed to a height of 4 feet, four by eight sheets of OSB all round the walls around his garage, to protect the walls against damage. His garage (about 18 by 21 feet) is part of his house and already has plasterboard walls and is insulated. So he will continue to meet fire regs and also protect the walls against the inevitable dings and bangs.

[John Rumm]

The rules for integral garages are very different. Especially if there is accommodation above them. A 1 hour firebreak actually requires more than 1/2" of plasterboard - two layers with skim are more typical.

Can be avoided if your sarking uses a breathable membrane.

[Stephen]

And that would avoid any losses (bridging?) through the rafters too.

Like you, I don't think an inch or two of lost height will be noticeable.

The only disadvantage will be fitting a light. Is that the same principle: very long screw through the sheet? I guess I'll have to mark where the joist are before I cover them, otherwise I'll be hunting for them forever.

Rusting (of drill bits mainly) is exactly the problem that has started me on this route. I see the FAQ recommends baby oil as the nearest thing to machine oil. Is that what you use, or is there somewhere to get machine oil from?

It's reassuring that 50mm will be thick enough. If I find something bigger as a second or on ebay (i.e. cheap) I will get it, but hopefully by sticking to 50mm it will keep the cost low.

Thanks again, Stephen.

[Stephen]

What resistance does 12 or 18mm of plywood give?

I thought kingspan/celotex types were much less flammable than polystyrene, which was one reason for chosing them.

That's interesting. On a different but related topic, my loft has four air bricks: two on either gable end. I suspect the two on one end are completely useless because there is cladding on the outside of that wall, which must reduce/stop any ventilation? There are no soffit vents.

When I laid rolls of insulation in the loft, I tried to keep them clear of the air bricks, but two bricks doesn't seem much for a loft to me but IANA expert.

However, looking along the street, none of the other houses has any air bricks at all. When one oft he neighbours had new soffits and fascias, he was told he did not need vented soffits. Why do none of the street have ventilation to their loft, and is my limited ventilation sufficient?

Thanks, Stephen.

[John Rumm]

In my workshop there were some cross beams in place anyway which make for ideal light mounting points. You could install a couple from rafter to opposite rafter before you insulate. (imagine the cross bar of a capital "A").

I fine with drill bits in the cases and humidity controlled with a little local heating and plenty of insulation it becomes a non issue.

Around these parts I can get 50mm at about £12/sheet.