Prefab steel building roofing sheet installation

[david.cawkwell]

Hi Group,

I am assembling the roof of a prefab steel building this weekend.

Never done this before so this may be a stupid question.

The roof sheet has highs and lows. I have hex head screws in the kit that will be long enough for the highs to reach the purlin below so that is fine. I also have shorter screws that will be used in the low sections of the sheet.

Should I only use the long screws I have on the roof leaving the lower parts of the sheet without any penetrations and therefore less leaks. Using the short screws on the walls. Or should I use some of the short screws on the low parts of the roof as well.

The hex screws all have a plastic type washer underneath the head so I assume this would stop water if I use them on the lows.

[Cicero]

================================== Standard practice is to put screws (with plastic caps if supplied) on the top of the corrugations only but make sure that your screws are long enough to get a good bite into the woodwork.

If you put them in the valleys they will almost certainly create a slow leak even if you use washers.

Cic.

[Tim Lamb]

In message , Cicero writes

Umm... The OP did not mention if the roofing sheets were an insulated sandwich. If so, the long screws should have a short length of thread below the hex head to pull the top sheet up to the sealing washer. On profile sheeting, they are normally fitted in the middle of the low section.

The short screws sound like stitchers used to stop water bouncing under the laps. Mastic tape supplied?

regards

[Andrew Mawson]

insulated

thread

...yes, sandwich sheets- 'composite roofing panels' have the cunning double threaded fastener - yesterday I put up 24 sheets on a shed roof - as you say shorter screws are supplied to stich the panel overlap and fix ridge and barge boards, but all have gel washers to seal. When I've put up uninsulated sheeting in the past the suppliers have (to my surprise at the time) told me to screw in the valleys not the peaks. But if you think about it, the valley is the only place you can pull the fixing tight without squashing the corrugations.

AWEM

[Tim Lamb]

In message , Andrew Mawson writes

How did you insulate the ridge?

I used fire rated expanding foam but found it a tad pricey. Elsewhere I tried cutting a wedge of foam.

How have you fixed the gutters and protected the exposed foam? Composite panel manufacturers do not seem to have solved this problem. I got some

4"x3" timber cut diagonally and made up some *Z* shaped brackets to attach to the top and bottom sheet. Clearly a different roof pitch will need a different wedge shape to provide a vertical gutter board.

regards