Ventilated vs un-ventilated garage roof.....
Discussion
Guys I know there is a wealth of experience and knowledge here so I figured it was worth asking this question.
I'm currently having a new garage designed to replace the leaking piece of turd I have at the moment. A friend who is an architect (I'm a steelwork draughtsman) is helping with the plans but he hasn't came across any of the roofing systems I'm looking at, at the moment. These have been EPDM, VM Zinc and now Alwitra. There's no option for non flat roof systems unfortunately.
The garage is going to be attached to the side of the house with a mono pitched roof at no more than 5 degrees.
I'm about to start draughting up the roof structure, each of the roof materials I've looked at have options for ventilated and un-ventilated structures. After doing a lot of googling I'm no wiser as to which way to go?!
If you go for ventilated i.e. creating a cavity do you need to provide drain points at the low end of the roof? or will there never be enough condensation forming to warrent it?
All minor details I know but need to figure out what's best early on to see how it affects clear height within the garage.
Thanks!
I'm currently having a new garage designed to replace the leaking piece of turd I have at the moment. A friend who is an architect (I'm a steelwork draughtsman) is helping with the plans but he hasn't came across any of the roofing systems I'm looking at, at the moment. These have been EPDM, VM Zinc and now Alwitra. There's no option for non flat roof systems unfortunately.
The garage is going to be attached to the side of the house with a mono pitched roof at no more than 5 degrees.
I'm about to start draughting up the roof structure, each of the roof materials I've looked at have options for ventilated and un-ventilated structures. After doing a lot of googling I'm no wiser as to which way to go?!
If you go for ventilated i.e. creating a cavity do you need to provide drain points at the low end of the roof? or will there never be enough condensation forming to warrent it?
All minor details I know but need to figure out what's best early on to see how it affects clear height within the garage.
Thanks!
At the moment there is no heating in the existing garage. Re-design will have double glazed door/insulated roller shutter door.
My plan with the new garage is to re-locate my boiler, water tank etc into it so it would be easy to heat it if required. The existing garage has major issues with condensation (pre-fab concrete panels with an asbestos roof) so I want to do whatever I can to avoid this.
With that in mind am I as well disregarding unvented construction now?
I read that the two longest sides of the roof should be vented, as one of the long sides of mine will be joined to the house (at the top of the mono pitch) is it acceptable to put vents in the shorter sides by overhanging the roof and putting in soffit vents?
Would the bottom of the pitch need vented/drain points or will condensation not be an issue?
Apologies for what's probably daft questions, I'm trying to maximise space (building on boundary line) and all these q's will affect eaves design.
VM Zinc are quoting 40 year lifespan vs Alwitra's 30 years, with that in mind do you think the additional cost is worth it?
Thanks.
My plan with the new garage is to re-locate my boiler, water tank etc into it so it would be easy to heat it if required. The existing garage has major issues with condensation (pre-fab concrete panels with an asbestos roof) so I want to do whatever I can to avoid this.
With that in mind am I as well disregarding unvented construction now?
I read that the two longest sides of the roof should be vented, as one of the long sides of mine will be joined to the house (at the top of the mono pitch) is it acceptable to put vents in the shorter sides by overhanging the roof and putting in soffit vents?
Would the bottom of the pitch need vented/drain points or will condensation not be an issue?
Apologies for what's probably daft questions, I'm trying to maximise space (building on boundary line) and all these q's will affect eaves design.
VM Zinc are quoting 40 year lifespan vs Alwitra's 30 years, with that in mind do you think the additional cost is worth it?
Thanks.
Any monopitch will last well above standard . Alwitra needs fitting very very well to last the course.
I don't see the point of the extra on Zinc unless aesthetic? Most premium flat roof coverings will last indefinately. (EPDM is not 'premium' by the way)
Personally, i would do a warm roof construction, your glazing will have vents in it. I would also put rooflights in , relativley inexpensive but make a world of difference.
Your options are limitless really. Budget will dictate, but there is a lot available for sensible money. Also worth remembering your 5 degree pitch can be achieved with firrings, the frame can go in square.
I don't see the point of the extra on Zinc unless aesthetic? Most premium flat roof coverings will last indefinately. (EPDM is not 'premium' by the way)
Personally, i would do a warm roof construction, your glazing will have vents in it. I would also put rooflights in , relativley inexpensive but make a world of difference.
Your options are limitless really. Budget will dictate, but there is a lot available for sensible money. Also worth remembering your 5 degree pitch can be achieved with firrings, the frame can go in square.
Edited by roofer on Sunday 30th December 12:59
Premium would be'
Permaphalt
Bauder/Iko Felt (plus some other manufacturers)
Sarna/Alwitra/Bauder T Plan Single Ply (when fitted by time served registered fixers)
Lead/Zinc/Copper are the ultimate but costly.
Green Roofing is coming down to sensible money, but i would only fit it on multilayer felt or Asphalt.
Most of the premium systems can only be fitted by regstered/licensed installers. The manufacturer then issue a full single point warranty.
Joe Bloggs can go and buy EPDM and fit it, good for us over the years as we've earned well removing it and putting proper roofs in its place. EPDM as a material is reckoned to last 50 years, probably will....but the bonding agents have no warranty whatsoever.
Permaphalt
Bauder/Iko Felt (plus some other manufacturers)
Sarna/Alwitra/Bauder T Plan Single Ply (when fitted by time served registered fixers)
Lead/Zinc/Copper are the ultimate but costly.
Green Roofing is coming down to sensible money, but i would only fit it on multilayer felt or Asphalt.
Most of the premium systems can only be fitted by regstered/licensed installers. The manufacturer then issue a full single point warranty.
Joe Bloggs can go and buy EPDM and fit it, good for us over the years as we've earned well removing it and putting proper roofs in its place. EPDM as a material is reckoned to last 50 years, probably will....but the bonding agents have no warranty whatsoever.
roofer said:
Any monopitch will last well above standard . Alwitra needs fitting very very well to last the course.
I don't see the point of the extra on Zinc unless aesthetic? Most premium flat roof coverings will last indefinately. (EPDM is not 'premium' by the way)
Personally, i would do a warm roof construction, your glazing will have vents in it. I would also put rooflights in , relativley inexpensive but make a world of difference.
Your options are limitless really. Budget will dictate, but there is a lot available for sensible money. Also worth remembering your 5 degree pitch can be achieved with firrings, the frame can go in square.
Zinc was my first thought as it would match a future extension to the rear of the house.I don't see the point of the extra on Zinc unless aesthetic? Most premium flat roof coverings will last indefinately. (EPDM is not 'premium' by the way)
Personally, i would do a warm roof construction, your glazing will have vents in it. I would also put rooflights in , relativley inexpensive but make a world of difference.
Your options are limitless really. Budget will dictate, but there is a lot available for sensible money. Also worth remembering your 5 degree pitch can be achieved with firrings, the frame can go in square.
Edited by roofer on Sunday 30th December 12:59
EPDM isn't really an option on an extension (as it looks pretty ugly whereas garage roof is hidden), whereas the Alwitra doesn't look too bad. Do you think there would be a massive difference in cost between the Zinc and Alwitra?
Funnily enough my FILs house has a huge Zinc roof on it but it was done in Ireland, it doesn't seem that popular a trade over here.
I'm now thinking I should put the whole roof design to one company, it's just a pain as I'm trying to bottom out eaves details before construction starts to maximise space.
jonnydrama said:
I'm now thinking I should put the whole roof design to one company,
Money for old rope. Give me your dims and i'll sort you a design to comply with Part L. Or PM and happy to talk you through any queries. A warm roof is easy, and makes sense if your going to the trouble of an insulated roller shutter.
If you are set on Zinc, i have one of the countrys foremost installers who travels a phone call away. (Cambridgeshire based)
Roofs are not a dark art, getting them at the right money is.
jonnydrama said:
Do you think there would be a massive difference in cost between the Zinc and Alwitra?
Alwitra cheaper.Edited by roofer on Sunday 30th December 21:43
I really, really appreciate that mate.
I've been on the VM Zinc website a lot of this evening looking at their typical details, most of which cover what I'm looking to do.
First week back at work I'll knock something up to send across to you for advice, I 'think' I'm getting the jist of it now
I've been on the VM Zinc website a lot of this evening looking at their typical details, most of which cover what I'm looking to do.
First week back at work I'll knock something up to send across to you for advice, I 'think' I'm getting the jist of it now
Is the roof insulated? Will there be ceiling linings or just exposed timbers?
By zinc/metal roofing I assume you mean a standing seam type roof on breather membrane and a plywood deck over the roof timbers? If so, there should be ventilation below the plywood deck. If the roof is insulated the ventilation should be above the insulation, below the plywood.
I would suggest that you do install insulation. If so the roof build up might look like this, starting from the outside...
Metal roofing
Breather membrane (preferably the type specifically designed for metal roofing
Plywood (EN 636 class 3 glue bond ideally (the 'new' WBP))
50mm ventillation void with 25 mm opening at eaves and 5 mm at ridge
roof joists/rafters with insulation between
Perhaps some more insulation below (like rigid foil faced boards)
Vapour control layer (polythene sheet)
Plasterboard (perhaps installed onto battens fixed through insulation if used).
Or perhaps I have totally mis-read the OP...
By zinc/metal roofing I assume you mean a standing seam type roof on breather membrane and a plywood deck over the roof timbers? If so, there should be ventilation below the plywood deck. If the roof is insulated the ventilation should be above the insulation, below the plywood.
I would suggest that you do install insulation. If so the roof build up might look like this, starting from the outside...
Metal roofing
Breather membrane (preferably the type specifically designed for metal roofing
Plywood (EN 636 class 3 glue bond ideally (the 'new' WBP))
50mm ventillation void with 25 mm opening at eaves and 5 mm at ridge
roof joists/rafters with insulation between
Perhaps some more insulation below (like rigid foil faced boards)
Vapour control layer (polythene sheet)
Plasterboard (perhaps installed onto battens fixed through insulation if used).
Or perhaps I have totally mis-read the OP...
Skodasupercar said:
Is the roof insulated? Will there be ceiling linings or just exposed timbers?
By zinc/metal roofing I assume you mean a standing seam type roof on breather membrane and a plywood deck over the roof timbers? If so, there should be ventilation below the plywood deck. If the roof is insulated the ventilation should be above the insulation, below the plywood.
I would suggest that you do install insulation. If so the roof build up might look like this, starting from the outside...
Metal roofing
Breather membrane (preferably the type specifically designed for metal roofing
Plywood (EN 636 class 3 glue bond ideally (the 'new' WBP))
50mm ventillation void with 25 mm opening at eaves and 5 mm at ridge
roof joists/rafters with insulation between
Perhaps some more insulation below (like rigid foil faced boards)
Vapour control layer (polythene sheet)
Plasterboard (perhaps installed onto battens fixed through insulation if used).
Or perhaps I have totally mis-read the OP...
Nope you've understood it perfectly and that's now what I'll be drawing out By zinc/metal roofing I assume you mean a standing seam type roof on breather membrane and a plywood deck over the roof timbers? If so, there should be ventilation below the plywood deck. If the roof is insulated the ventilation should be above the insulation, below the plywood.
I would suggest that you do install insulation. If so the roof build up might look like this, starting from the outside...
Metal roofing
Breather membrane (preferably the type specifically designed for metal roofing
Plywood (EN 636 class 3 glue bond ideally (the 'new' WBP))
50mm ventillation void with 25 mm opening at eaves and 5 mm at ridge
roof joists/rafters with insulation between
Perhaps some more insulation below (like rigid foil faced boards)
Vapour control layer (polythene sheet)
Plasterboard (perhaps installed onto battens fixed through insulation if used).
Or perhaps I have totally mis-read the OP...
Good, HTH.
Have a look at the metal roofing manufacturer's standard details. You should find something similar to what I just posted. Sounds like you have been looking already though.
Someone mentioned warm roofs (i think). You could go warm roof, but it might mess up ridge height. A warm roof is where all the insulation is above the roof joists (rather than between/below). I don't personally see the point of going this route with a garage as it is extra cost and more tricky, although it is 'better'. But with a warm roof setup, you would still need some ventilation below the plywood deck to keep it in good condition.
British Standard BS5250 is the place to look for guidance on roof ventilation requirements, although you will probably struggle to find a copy for free.
Post up some drawings and I am sure there will be some useful tips and guidance.
Have a look at the metal roofing manufacturer's standard details. You should find something similar to what I just posted. Sounds like you have been looking already though.
Someone mentioned warm roofs (i think). You could go warm roof, but it might mess up ridge height. A warm roof is where all the insulation is above the roof joists (rather than between/below). I don't personally see the point of going this route with a garage as it is extra cost and more tricky, although it is 'better'. But with a warm roof setup, you would still need some ventilation below the plywood deck to keep it in good condition.
British Standard BS5250 is the place to look for guidance on roof ventilation requirements, although you will probably struggle to find a copy for free.
Post up some drawings and I am sure there will be some useful tips and guidance.
I guess a bit of a cross post there.
Yes, insulation between and/or below the rafters is a cold roof. Insulation (ALL of it) above the rafters is a warm roof. Differences are thickness of the roof buildup for a given U-Value and sometimes (dependent on roof buildup) different requirements for ventilation. Warm roofs are generally considered best practice, but there are a lot of variables and for many/most applications a cold roof is fine. Flat roofs are different, and should be constructed as warm roofs whenever possible.
Many people think that a warm roof is a habitable roof space, and a cold roof is just a normal loft. This is incorrect. It is to do with the placement of the insulation in relation to the structure.
Yes, insulation between and/or below the rafters is a cold roof. Insulation (ALL of it) above the rafters is a warm roof. Differences are thickness of the roof buildup for a given U-Value and sometimes (dependent on roof buildup) different requirements for ventilation. Warm roofs are generally considered best practice, but there are a lot of variables and for many/most applications a cold roof is fine. Flat roofs are different, and should be constructed as warm roofs whenever possible.
Many people think that a warm roof is a habitable roof space, and a cold roof is just a normal loft. This is incorrect. It is to do with the placement of the insulation in relation to the structure.
From the additional digging I've done today it'll probably be a cold, ventilated roof as I'm already struggling with height constraints. Like this:
I will see what fits though
edit: I can get British Standards for free through work, I'll grab that one when I get back
I will see what fits though
edit: I can get British Standards for free through work, I'll grab that one when I get back
Edited by jonnydrama on Sunday 30th December 23:45
That roof construction looks just fine, and the sort of thing you should be looking to construct.
Make sure when you purchase the plywood, you pay decent money for a decent product. There is LOADS of s
t plywood on the market. If it seems really cheep, it will almost certainly be no good at all, regardless of what it is being sold as.
Make sure when you purchase the plywood, you pay decent money for a decent product. There is LOADS of s
t plywood on the market. If it seems really cheep, it will almost certainly be no good at all, regardless of what it is being sold as. Skodasupercar said:
Good, HTH.
But with a warm roof setup, you would still need some ventilation below the plywood deck to keep it in good condition.
No, you wouldn't. A warm roof is encapsulated, with a vapour barrier as the first layer. No additional ventilation is required. Furthermore, OP has a monopitch, so ridge height not an issue. You can lose 120mm in fascia depth.(Current U value required )But with a warm roof setup, you would still need some ventilation below the plywood deck to keep it in good condition.
So I guess something like this is also an option? http://www.vmzinc.co.uk/build-zinc-systems/standin...
As you don't need a ventilation gap there can't be much between the two roof heights I guess?
As you don't need a ventilation gap there can't be much between the two roof heights I guess?
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