metal box profile questions

seneca · 9 Oct 2007

Hi,
was wondering if anyone could help me out with my plan for a new roof for an old shed. I have a 3m x 5m shed with a pitched roof and am looking to cover it with metal profile. The triangles that make up the roof are sound and have been reinforced, just need to add purlins to lay the sheets on. my questions are:
1) should I use metal profile or some other form of roofing, if so what?
2) what are the pros and, more importantly, cons of metal profile?
3) being metal, will it make a lot of noise in the rain, when i am inside?
4) will i get lots of condensation dripping down from the inside the roof? if so, how can i avoid it.

The reason I'm going for metal profile is it's cheap, easy to install and I can get it done quickly before the bad weather really starts. Also, the shed is under a few trees and will get lots of tigs, acorns etc landing on it. I thought metal would be best as it should be able to withstand any damage. (It also comes in a nice brown colour that matches the sides.)

masona · 9 Oct 2007

I did my summerhouse with moisture resistant chipboards then roofing felt with the metal sheeting on top so condensation will run onto the felt via the gutter and also it helps the sound barrier. Not sure what you mean about the purlins and don't know which way your pitch roof is, any photo?

Deluks · 9 Oct 2007

Condensation will only be a real problem if your shed has little ventilation and a source of moisture. You could use Masona's method but could just use slaters underfelt stretched tight over the rafters before laying the sheets to save the extra expense of boards.

I think the metal sheets would be the best option considering the tree issue, although corrugated bitumen sheets are cheap and will still have a decent lifespan.

marshman · 9 Oct 2007

how far apart are your triangles as you called them ?
cons of metal roofing sheets every hard frost they freeze on the inside when defrosting they drip water.
condensation on cold mornings keep the shed damp inside, heat like a oven in summer,
ear plug nearly needed in a hail storm.
I similar to Masona lined my roof with 2400x1200x18mm water proof ply "safe to walk on" then felted
then screwed the sheets to that.
my shed is only 3x4m flat roofed "well a foot fall"
I have two 150x50x4m purlins then counter batten at 400mm centres under ply
you can get insulated metal profile.
you also get plastic profile the same as the metal that goes on first then insulation then the metal profile
is fixed over this.
I think the purlins for metal profile is 1200mm.

seneca · 10 Oct 2007

soory about the"triangles" reference, didn't know the technical name. I assume purlins are the straight bits of wood that run across the sides of the "rafters?" and the sheets are attached to these. I looked at an old garage and saw they used 3 purlins. One near the apex, one in the middle and one near the gutter. I had planned to do that.
I like the idea of stretching felt across the rafters, as I don't think I have the time, or the budget to put a layer of 18mm ply on first. Also, It might make the roof too heavy. I have already used too much wood on the roof frame, and with the weight of the profile, don't want the thing to collapse on me.
I planned to put a thin layer of ply on the underside of the roof (the bit facing inside) next summer, and maybe some 25mm polystyrene insulation as well. But that would be regular, chap 6mm stuff, and next summer (fed up of working in the rain & cold

)
Will try to get a photo, if I can get the camera working, but then there's the problem with uploadiong (I'm as handy with a computer as I am with DIY!)
thanks folks.

masona · 10 Oct 2007

seneca said:
I looked at an old garage and saw they used 3 purlins. One near the apex, one in the middle and one near the gutter.

The top is the ridge, the middle is the purlin and the bottom is the wallplate

marshman · 10 Oct 2007

seneca said:
soory about the"triangles" reference, didn't know the technical name.

roof trusses

I use 18mm as I need to stand up there on steps to service washing line, "new pull rope through pully".

(fed up of working in the rain & cold )

Ha know that feeling

seneca · 16 Oct 2007

hi folks,
using deluks' idea of

"stretching slaters underfelt tight over the rafters before laying the sheets"

I've managed to get hold of some breathable roofing membrane (left over from some work a freind had done) which I think is waterproof. I plan to stretch this over the rafters and staple it down. Then I will lay three battens/purlins horizontally across the length of the roof and attach the metal sheets to this. Will that be ok? any suggestions?

couple of things I'm not sure about:
1) looked at manufactures website and they say it should not be stretched tight, but allowed to sag by 1.5cm to form a gutter. problem is I have noogins between rafters which won't allow that. what should I do?
2) with my battens/purlins running horizontally across, won't they stop any condensation from rolling down? Presumably, once the water drips onto the felt it will run down the slope of the roof, but hit the batten/purlin on the way down and stop
3) the manufactures say any overlap should be sealed with jointing tape. What is that? and is it easily available? can't find a mention to it anywhere. is it basically, double-sided sticky tape that goes between the 2 sheets of felt?

any advice would be appreciated

Deluks · 17 Oct 2007

All that advice applies to tiled roofing, and doesn't matter for your application.
Over 3 metres go for 5 or 6 purlins (from now on shall be known as battens)
The battens will give an airgap between the membrane and underside of roof, this gap should be kept open using air vents in weatherboard/fascia boards, this will help the timber dry out should it become wet from excess condensation.

or you could use thin vertical battens on the rafter tops, over the membrane, then horizontal battens over these for fixing the metal sheets to, this will allow condensed water to flow down the membrane and out.

seneca · 19 Oct 2007

thanks Deluks. finally got everything; now just need to get up there and do it! (sheets now have frost on them and I can't find my gloves

)

looking at various websites I see a lot of people use "foam fillers" which match the profile and keep the wind out. They fit between the sheet and batten. Anyone ever used these? and are they worth while, bearing in mind there will need to be a gap beneath the batten to let the condensation run out.

When overlapping the sides of sheets you are meant to join the sheets together with small screws called "stitchers." Is it also worth putting a line of silicon sealant down on the overlap, and then stitching the sheets together?

drewroof · 20 Oct 2007

the use of foam fillers is reccommeded, and under the ridge, this will keep out the birds and wind,

the stitchers should be fixed every 450mm with a bead of 3mm mastic strip under the lap (this comes on a 9 metre rool)as this will help in windy conditions,and will help keep condensation out

seneca · 21 Oct 2007

with a bead of 3mm mastic strip under the lap (this comes on a 9 metre rool)

is that the same as double sided tape? not sure what it is or where to get it. is it available from one of the diy stores?

should have mentioned that the metal profile has ridges on it to give the effect of tiles. therefore there are no long flat parts to smoothly apply tape. thats why I was thinking about a thin strip of silicon sealant. will that work, or should I use some kind of double sided tape.

cheers.

drewroof · 21 Oct 2007

http://www.cglass.co.uk/product.php?productid=16921&cat=416&page=1

thats the kind of stuff you need,

you put it where the sheets overlap when you lay them,

drewroof · 21 Oct 2007

this is a good reading for you if your not sure,

http://www.cladco.co.uk/install.htm

drewroof · 21 Oct 2007

incidently i noticed you are in the west mids, where about? if your close to me i could pop round and give you a few pointers, plus i also have the sealant strip and some fixings down me cellar some where

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metal box profile questions

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