Anyone have experience / advice re garage roof insulation?

[J.B. Welding]

Heeyyyy..auto correct on Scottish slangy words-like it! Pi$h? (testing)

 

[skotl]

you can buy vents for the facias they are about 50mm round drill with hole cutter and push them in !

33p from wickes

Groovy - that's where I'd be getting the board from!

 

[Kent]

Not sure about ignoring both bits of the manufacturer's advice! Are the 3x2s short battens between the rafters? If so then nope - none of them! However I could put them in after I mount the boards, both to reinforce and hold the boards up.

If there is no space you get no venting issues. I should rather have the 3x2" personally speaking. Nothing was vented in the 70s and CHeating became the norm, this created tremendous issues with roofs and buildings in general, it now gone to overkill IMO. No space=no air and well insulated with foam boards the outer skin wont be so cold inside either as to attract interdental condensation to form anyhow. The venting on a flat roof wont stop it it will just help dry it up after it forms (not all days have the airflow)

 

[Kent]

Kingspan is what the builders use , and vent the soffit's with a few holes and stick the soffit vents in !

Same basic product different trade name that's all, kingspan spend more on marketing but I bet there are at least half a dozen products that are identical

 

[p0689109]

Cheers. And it's just a hardboard roof with felt, so no weight up there.

There is a canny bit of weight on there when it snows!!

 

[AndersK]

150mm Rockwool in the walls and 250 in the roof in my garage, coolest place I have in summer time

I use this for venting on my house. Fits under the tiles or sheet, about 2,5 pounds

 

[Migmac]

What about using bubble wrap?

 

[Rig Pig]

I filled mine with glass wool & stapled some silver foil faced bubble wrap that's allegedly equivalent to 25mm of poly board over the top, I left a small gap at the edges of the soffit for ventilation. No rust or condensation last winter and a nice cozy workshop with minimal heating.

 

[Kent]

I filled mine with glass wool & stapled some silver foil faced bubble wrap that's allegedly equivalent to 25mm of poly board over the top, I left a small gap at the edges of the soffit for ventilation. No rust or condensation last winter and a nice cozy workshop with minimal heating.

Some of those foil blankets have a better U value than the thickest Foam foil boards if you research them and fit with foil tape to the joints

 

[skotl]

I now have a plan. which combines much of the advice on here.

I have ten runs of around 3.3m each. Going to put the 25mm celotex up there,with a 50mm air gap and drill a 50mm hole at the end of each run and install one of these;

...and use silver tape to seal the Celotex to the rafters.
I can get the Celotex on offer from Wickes at around £100 and the soffit vents are 33p each.

I appreciate all the advice and I know that there are a bunch of alternative options and opinions, but this seems a relatively low-cost option and less effort than faffing about with wool and plywood.

My only remaining question is considering each 3.3m run and the ventilation - do you think that a hole at one end is enough or should I put another one in at the other end? Extra cost would be £3.30 for ten extra vents

Cheers

 

[Kent]

Not talking bubblewrap foil stuff people put behind radiators and the like but the inter layered stuff with fibre BBA cert and tested as in the Building regs. Simple to measure as a U value one product against another.
Talking insulation though its down to its weakest part like an open door, there is lots on the net about this if you read up on passive houses etc.
Garages and workshops though ? heck if you need to make them warm your not working hard enough

 

[skotl]

Not talking bubblewrap foil stuff people put behind radiators and the like but the inter layered stuff with fibre BBA cert and tested as in the Building regs. Simple to measure as a U value one product against another.
Talking insulation though its down to its weakest part like an open door, there is lots on the net about this if you read up on passive houses etc.
Garages and workshops though ? heck if you need to make them warm your not working hard enough

It's not for warmth - the single brick walls and the up-and-over garage door pretty much kill that idea off!
My aim is to keep the humidity down and received wisdom is that insulating the roof can help this.

I installed a dehumidifier a few weeks back and I'm amazed that it's removing probably 1-2 litres of water a week, in a relatively warm spring. I shudder to think of the humidity in the winter.

Next plan will be what to do with the door, but that's another thread / month!

 

[skotl]

Cheers, mr fuzzy. I suspect it was your post in the "Rust!" thread that sent me toward insulating the roof.

I also plan to have a couple of larger vents on the wall, and I need to sort out the pee-through-the-wall mod for the dehumidifier.

as an aside #1... it's amazing what you don't realise you don't know about all sorts of topics! Humidity, insulation, ventilation, air gaps, etc. I'm enjoying the learning experience.
as an aside #2... most of my projects seem to be about making my workshop a better environment to... ummmm... well, I'm enjoying making a better workshop

 

[skotl]

That is cheap!

I'm going to go ahead with the celotex for the roof as I think that's where most of the heat is lost.
But polystyrene might be the way to go for phase ?3? (in that the door may be phase 2).

I must admit to feeling uncomfortable at the though of the pyro-magnet that polystyrene is, though. I suspect that if a panel caught alight then the entire garage would be rubble in seconds

 

[Migmac]

The beauty with bubble wrap is, if you get bored or work gets lean you can sit and pop the bubbles

 

[Rig Pig]

Not talking bubblewrap foil stuff people put behind radiators and the like but the inter layered stuff with fibre BBA cert and tested as in the Building regs. Simple to measure as a U value one product against another.
Talking insulation though its down to its weakest part like an open door, there is lots on the net about this if you read up on passive houses etc.
Garages and workshops though ? heck if you need to make them warm your not working hard enough

I'm eyeing that stuff up for a loft conversion, it looks very promising for above rafters to keep as much headroom as possible.

The silver bubble wrap in my workshop was from eBay and was a very cheap alternative vapour barrier, I was dubious of its insulation quality however at the price it was well worth it, it is definitely better than plastic film.

 

[Kent]

I'm eyeing that stuff up for a loft conversion, it looks very promising for above rafters to keep as much headroom as possible.

The silver bubble wrap in my workshop was from eBay and was a very cheap alternative vapour barrier, I was dubious of its insulation quality however at the price it was well worth it, it is definitely better than plastic film.

Its very good but don't try screws the fibres grab the shank and break the screws. Local building control will most likely insist on foam boards and one such product as the muti layer foil (that actually out performs the boards)