Boarding a ceiling with OSB

[jimbo84]

The garage is just over 10 years old and has a pitched roof with the premade type of trusses and the ceiling is partially badly boarded with various bits of thin chipboard by the previous owner, everything is uninsulated. It's all sagged so taking the lot off and fully boarding with 11mm OSB with the intention of insulating with the fibreglass loft roll insulation.

I've put 2 boards up for now (that was good fun on my own) but it has just dawned on me should there be some kind of vapour barrier behind the OSB?

I'm also boarding and insulating the single skin brick walls by building some stud walls and taping in PIR before boarding with the OSB so the walls will have a vapour barrier anyway, it's just the ceiling I was wondering about.

Various stuff online saying do and don't but I know someone on here will have done it previously and will know for sure, thanks.

 

[gaz1]

yes it will be fine just put a joint wood at side of a join so you can get a better grip to screw on

if your wondering why its either side its so that it can be insulated but if you want use plastic netting and leave the roll up there pre partial rolled out

 

[dieselsamurai]

Depending on the thickness of the rafters fiberglass roll will not be the best option PIR would be better if they are not very deep but obviously more expensive

 

[dieselsamurai]

Needs to be quite deep , depends what you are expecting to achieve by insulating

 

[dieselsamurai]

may be useful , I know for a house but you will need an air gap too it being a cold roof design so will need air flow ideally

 

[gaz1]

id rather use fibreglass

 

[dieselsamurai]

there are always pro and cons.... id rather use it too but 75mm of it doesnt do much all the cielings in my house have rockwool in them for the above reason

 

[Erie Fred]

It's popular in the states to use corrugated steel roofing for the ceiling.
At 29 ga it is quite light.

 

[Brad93]

Advantage of PIR is it doesn't get damp or rot.

You can also aluminium tape the gaps between the rafter and the pir board to make it air tight and act as a vapour barrier.
You will need airflow on the backside if there is a void. Either some vents in the eaves or in the ridge.

 

[jimbo84]

Thanks everyone. I think I might have confused things by saying a pitched roof, it is the ceiling joists I'm boarding/insulating, there'll be a loft space up above.

I haven't bought the insulation for the ceiling yet so I could go PIR, it's just the cost, but with it being a loft space there is unlimited room for fibreglass insulation so I could pile it up. I have some stuff up there I store but once the ceiling was done I was going to rearrange/make it better anyway.

There aren't any eaves vents at the moment but it was my intention to put some in to ventilate the loft space once the ceiling is boarded.

This was the first board up. the gap to the right is where the new wall will be, it's not visible but the board finishes on a joist to the right, the gap is shorter for the last joist.

 

[addjunkie]

For putting sheets upon your own, hire or borrow a plaster board sheet lifter.

Amazon.co.uk : plasterboard lifter

 

[Keith 66]

Advantage of PIR is it doesn't get damp or rot.
You can also aluminium tape the gaps between the rafter and the pir board to make it air tight and act as a vapour barrier.
You will need airflow on the backside if there is a void. Either some vents in the eaves or in the ridge.

When i replaced my garage roof a few years ago it was done with insulated profile steel sheets, the insulation is 40 mm expanded polystyrene on the flats between the profiles. I have noticed that the roof is not quite as efficient as the 35mm PIR offcuts that were stuck straight to the underside of the old corrugated asbestos roof. It takes longer to warm up with the oil filled rad. However all round efficiency is probably up a bit cos the doors & all leaks are fixed.
What i have found is that poxy mice used to tunnel in the old PIR foam & i could hear the little buggers munching away. This led me to sitting there with an air pistol trying to work out where they were & taking potshots! Dont think i ever hit one.
Also Ants like tunneling in the stuff too & will hollow it out big time, I have them in a few of the wall cavities.
In hindsight i should have gone for 70mm or Pir insulation but its too late now.
Its worth going with pir if you can afford the increase.
Still on the whole its nice going into a nice warm dry workshop!

 

[jimbo84]

For putting sheets upon your own, hire or borrow a plaster board sheet lifter.

Amazon.co.uk : plasterboard lifter

That would make life a lot easier. I only have 3 more boards to do and I’ve made a hook that hooks to the ceiling joist at one end, I can hook one edge of the board under that, lift up the other edge and then get my prop under to secure it before screwing it up.

 

[voipio]

Are there any plans to insulate the door, and also close up some of the gaps around the door?

 

[Erie Fred]

IIRC Snowball engineering just did something similar:

 

[jimbo84]

Are there any plans to insulate the door, and also close up some of the gaps around the door?

Yeah I've got some seals for the door edges and I'll be backing them with 25mm PIR.

 

[gaz1]

this stuff allows you to go right up against the wall instead of a 1" gap

it can be used instead of slaters felt

BASEMENT TANKING CAVITY DRAIN MEMBRANE KIT 2MX20M D/S TAPE & 100 PLUGS & SEALS | eBay

The 8mm stud height minimises problems caused by raised floor levels. It is highly resistant to water, alkalis, saline solutions and organic acids, and is not affected by minerals. It is also resistant to bacteria, fungi and other small organisms.

www.ebay.co.uk