Felt for shed roof?

[The Medway Handyman]

Trying to find an accurate way of estimating how many rolls of 1 mtr wide felt you need for given sizes of apex & pent roof sheds.

Google is not my friend :-(

Any sites?

[JoeJoe]

It shouldn't be too difficual to put together a simple Excel sheet to do that.

[The Medway Handyman]

If I knew what the angles were...

[Dave Plowman (News)]

Fairly simple maths.

If you draw a line from apex to base of the roof you form two right angle triangles. And the formula for working out the longest side of that - ie the part which is covered in felt - is schoolboy stuff.

Ie the length squared equals the sum of the other two sides squared, for a right angle triangle.

So with your handy calculator, square the height of the apex and add that to the square of *half* the width. The square root of this gives you the length of one side. Double that and multiply by the length of the shed gives the area of the felt.

[dennis]

Why do you need the angles?

[george (dicegeorge)]

draw a scale diagram, perhaps on squared paper.

[g]

[Dave Plowman (News)]

Badly put. The length squared of the side opposite the right angle equals the square of both other sides - then added together.

[John Rumm]

20 deg pitch is about right for an apex. Many pent roofs will be very shallow - for estimating purposes I would treat them as flat and add say 5% just to be on the safe side.

[Roger Mills]

That will certainly give you the roof *area*. But there's a bit more to it than that when it comes to estimating how much felt you need. The fact that the OP mentions *rolls* (in the plural) suggests that he's talking about big sheds - so overlaps need to be taken into account. And then, of course, the felt needs to be extend beyond all the edges, and folded underneath - so you need to allow for that, too.

[Andy Dingley]

Don't need them. Measure width & height, then use Pythagoras. Linear measuring is usually easier than angles.

[dennis]

You don't need Pythagoras either.. just measure the roof. If you can't reach, measure a few feet down at the ridge and the eaves, mark the distance on the walls and measure them as it will be the same.

[Steve Firth]

I suggest working it out with a pencil. Or going into a builders' merchants and asking if he can get felt.

[Man at B&Q]

Customer "Can I have an estimate to re-roof an 8' x 6' shed please?" TMH "Yes, the call out fee for coming to measure the roof will be =A340"

Not the cleverest way to run a business, eh?

MBQ

[The Medway Handyman]

Because the roof of an apex shed is larger in area than the shed.

[The Medway Handyman]

But people don't know the height of their sheds, they just know the length & width.

[The Medway Handyman]

Thats exactly it. I don't want to go & measure. The customer only knows the length & width as you say "an 8' x 6' shed".

[The Medway Handyman]

But you still need the height - and the punters don't know it, they simply know they have a 10 x 12 or a 10 x 8 shed.

[The Medway Handyman]

Don't give up the day job...

[Harry Bloomfield]

The Medway Handyman explained :

Probably because it is not an easy thing to calculate.

Measure out the length, end to end including the overhang - work out how many of these lengths you can get out of a roll. Count the number of lengths needed - per side of the apex and double it, Like this...

Allow a 4" overhang for the bottom one, allow a 6" overlap for each layer and then a final 9" over the apex from each side. Sometimes it can work out better - in that a lengthwise fold along the centre of a length can be placed along the apex and still give proper cover down to the top most layers on each side.

[dennis]

So you can't work out the answer then.

You may as well guess.