cold roof insulation questions

[GlennSpray68]

Hi All ,
Great forum BTW lots of lost hours reading many differing posts amazing what you can learn .

My situation is as follows .
I have a 1960's semi with a brick single skin attached garage with a concrete floor which slopes severely back to front approx 8" fall over 12' and a cold flat roof.the garage is sized at 7' wide by 25' long .
I am wanting to insulate the garage to make it warmer in the winter to use as a workshop /gym etc, but not a habitable room.
I have read as much as possible with regards to insulating and damp proofing but still have several questions which are as follows .


The roof ( whole can of worms this is !!) I have 19 4X2's running perpendicular to the length of the garage I think this means that if I insulate it with 50mm kingspan then dry line with foil backed plasterboard and leave a 50mm air gap above the insulation I will have to put in 34! vents (17 on each side)
which I am obviously trying to avoid.

Would it be permissible to run two lengths of 40mm waste pipe below the ceiling level with a t section and a small upright going to the ventilation space above the insulation at each joist space centre and vent it externally at either end of the garage or have a fan to push air through the pipes to take away any moisture. I do not want to drill through each timber as it will obviously weaken them

Or Is there anyway I can fully insulate the ceiling to make it a solid block of insulation then put a vapour barrier up and finally line it with plasterboard? as this will make it a lot simpler for my aching brain .

Lastly what is the minimum vent size I would require if i decide to drill through the sofit and bricks

If anyone can help with these questions I would be very grateful .

Many thanks in advance for any help and sorry for the multiple questions

Glenn

 

[freddiemercurystwin]

Well, get this, if this were a bona fide gabrage conversion and the garage was sandwiched between two properties, Building Control would let you stick insulation in between the joists hard up against the underside of the deck with no ventilation at all. Its not ideal but will probably be ok.

 

[GlennSpray68]

Thanks for that Freddy, I don't know how you can have one requirement for that scenario and not be able to duplicate it elsewhere ? strange me thinks

 

[freddiemercurystwin]

Because (again if you happen to be doing a proper by the book conversion) there is scope within the Regulations such that you should do all that is reasonable where a conversion is concerned, if the other option were to be remove the roof covering and create a void or add insulation on top to create a proper warm roof set-up then that could be deemed unreasonable. As mentioned it is not ideal but will probably be OK. At some point your roof covering will need replacing and the issue can be more economically and more easily addressed then. There is a risk of condensation but that’s the chance you take and let’s not forget you’re just making a workshop a bit more comfortable not creating a new living room for the family.

Venting every void at each side or some kind of Heath Robinson set-up seem unreasonable/excessive to me for an outbuilding.

 

[GlennSpray68]

Here , here !!

Thanks Freddy thats really helpful, can get started now !!

all the best

Glenn