Fitting Roofing Felt

[Gina]

As a corollary to the other thread about roofing materials I thought I'd start a thread about roofing felt and how to use it.

Several questions arise :-

1. Providing support for the roof - roof joists, size and how many.

2. Support for the felt, OSB, plywood, thickness.

3. Which way to arrange 8x4 sheets - viz. join across or down the slope.

4. Similarly for the felt - which way round - across or down the slope.

5. Fixing the felt down - clout nails v adhesive.

6. The joins - amount of overlap, adhesive?

The timber yard I'm buying my timber from said OSB was what they use for their sheds. And for an 8ft square (or smaller) roof, 11mm thickness quite adequate. If adequately supported, of course, which takes us to question 1. above.

[Freff]

Hi Gina.

I'll try and answer some of your question by how I done my workshop and now my obsy.

1...For my obsy I used 20" centres for the joists, this would help in the rigidity of the roof from twist later.

2...OSB is what I used. It's about as strong as ply, a lot cheaper and has good bitumen adhesive properties.

3...My roof is 14' long so I went length ways with the OBS, again for rigidity, and to avoid twist.

4...Length ways.

5...I used hot bitumen and clout nails. Felt laid at the bottom of roof first. Clout nailed along the the edging then overlapped by the next layer working towards the top.

6...As above. The felt usually has an edge that is uncoated for joining.

Note.

I used 18mm Ply on my workshop (OSB not available then) and I'm using 8mm OSB on my obsy. The reason for 8mm is because I'm also roofing with steel profile.

[laser_jock99]

1. Providing support for the roof - roof joists, size and how many.

We used 2"x2" @ 50cm spacings

2. Support for the felt, OSB, plywood, thickness.

11mm sounds okay

3. Which way to arrange 8x4 sheets - viz. join across or down the slope.

Probably doesn't matter too much.

4. Similarly for the felt - which way round - across or down the slope.

Longitudinally - starting at the bottom working to the apex. Allow plenty of overhang to nail down.

5. Fixing the felt down - clout nails v adhesive.

Both. Completely coat the OSB with adhesive (this will help waterproof it and hold the felt on). Nails worth doing along the joints.

6. The joins - amount of overlap, adhesive?

Min 6" overlap, plenty of adhesive + nails.

Having repaired a few storm damaged roofs the belt & braces approach is best.

[Gina]

Thanks for your answers

[ncjunk]

Not a very complete answer but-

I painted the roof in bitumen paint and then put the felt down on top of the bitumen using it to glue it in place. I overlaped the felt by a couple of inches and then nailed four battons across the felt and tacked around the edges.

Just tacking or nailing it down wont work here as the winds are too strong. I used ply, cant remember the thickness, for the roof sealed and then painted the ply...felt on top of that.

The felts not going anywhere but the whole roof might...still not fixed in place.

[noakesy]

i need help to build a warm room any one local fancy it s/wales

[fwm891]

I used 18mm sheathing ply as a roofing material with 3x2 cls supports every 600 mm. I glued (bitumen adhesive) the felt in place no nails or tacks, (ops its under felt the proper stuff never got used!) and thats been there 10 or more years - must get round to finishing that before I move house! Only one thickness of felt applied.

There's about 100mm overlap at joins and I ran my felt along the length of the roof working up the slope so the upper piece overlaps the lower