roof fall on a garden room

[freddiemercurystwin]

You should ensure you end up with a minimum 1:80 following any sag. Don't build it with 1:80 because you'll end up with less eventually.

 

[mrrusty]

I’m a bit tight for head room in here

Unless there are specific reasons not to, why don't you pay the £3-400 and get planning so you can go a bit higher? You can get planning with hand drawn drawings and downloadable location plans. It isn't difficult.

A very low ceiling is IMHO oppressive and spoils much of the benefit of having the extra space.

 

[Jupiter01]

You make a very valid point re. Planning permission @mrrusty. I’ve not done it due to time and expense to be honest. Was planning to have this complete before the winter sets in.

I am not proposing that I use 4x2s for the roof. Will definitely be using 5x2s but was checking whether the extra timber at the front could be less than 50mm. Clearly as this roof slopes down to the back, the ceiling space will be reduced.

 

[nickjb]

Just make it 50mm higher at the front. Nobody is measuring it with that level of accuracy.

 

[Jupiter01]

I plan to calculate my 2.5m from the ground up to this second top plate on the front (giving me the 50mm slope). The back wall will be 50mm lower than this.
Since I am extending the front roof by 40-50cm, that will take me slightly over the 2.5m at the edge of this extended roof. Wil that matter do you think?

 

[Jupiter01]

Just fix one wall plate higher. Minimum fall for an EPDM roof is 1:80 but this is the absolute minimum so I wouldn't skimp on joist size as you wouldn't want a puddle in the middle, thinner (than 18mm) OSB decking is fine, my garage has 9mm with joists at 400 centres and I haven't gone through it yet.

I was going to go with 11mm OSB on the roof with 5x2 rafters at 400 centres. Will that be okay for me to walk around whilst I am fitting the rubber roof?

Also, do I need to leave expansion gaps when installing this OSB board on the roof? Apparently its required for the floor...

 

[Jupiter01]

I was going to go with 11mm OSB on the roof with 5x2 rafters at 400 centres. Will that be okay for me to walk around whilst I am fitting the rubber roof?

Also, do I need to leave expansion gaps when installing this OSB board on the roof? Apparently its required for the floor...

Can someone give me a steer on this please

 

[mrrusty]

Yes you need a small gap between OSB sheets of about 3mm to allow for a little expansion. I think I would prefer 15mm OSB TBH.

 

[Jupiter01]

Yes you need a small gap between OSB sheets of about 3mm to allow for a little expansion. I think I would prefer 15mm OSB TBH.

Just a 3mm gap on both floor and roof OSB? No need for foam or any other substance in this gap.
Happy to go with 15mm OSB for the roof

 

[chirpychippy]

I build them with 4x2 walls, front and back walls are 400 centre studs, side walls are 600 centre studs.

The roof load is front to back.

I set the studs at 2.44 centres externally for osb to reduce waste on the 11mm osb.

With a 3mtr span I would use 6x2 c24 then add 70mm to 0mm Firrings front to back.

You could however incorporate the fall in the joists by packing the front plate by 70mm, but internally your ceiling won't be flat, it will be slanted. Over the joist I would use 18mm osb 3. I prefer T&G Boards.

Put the joists directly above the 4x2 studs of the stud wall for maximum structural strength.

Leave the pipe work below surface until the building is weathered.

Enjoy yourself, they are fun to build.

 

[Jupiter01]

I set the studs at 2.44 centres externally for osb to reduce waste on the 11mm osb.

I don’t follow this part? Are the studs not 400 centred for the plasterboard and hence need the OSB to be trimmed?

With a 3mtr span I would use 6x2 c24 then add 70mm to 0mm Firrings front to back.

In another post the guys suggested that 5x2 with a 50mm lift at the front should be adequate? I am trying to maximise the ceiling height internally.

Also should I leave a 3mm expansion gap in the osb lining too or is this affecting the waterproofing?

 

[chirpychippy]

I don’t follow this part? Are the studs not 400 centred for the plasterboard and hence need the OSB to be trimmed?

OSB is about £14 a sheet, plasterboard is about £9.00 a sheet, its just a cost saving exercise.

In another post the guys suggested that 5x2 with a 50mm lift at the front should be adequate? I am trying to maximise the ceiling height internally.

Trada Span Tables. If you use C16 at 400 centres you definitely need 6x2, 5x2 at C24 is still a fraction undersized, about 30mm.
Will probably be OK, but id still go 6x2 as it'll definitely be OK.

Also should I leave a 3mm expansion gap in the osb lining too or is this affecting the waterproofing?

Around the walls I wouldn't bother. On the roof, it depends on the finish, often times the boards are butted if square edge with a 10mm expansion gap around the perimeter, T&G take care of themselves.

 

[Jupiter01]

My side wall needed to be 215cm with one base plate and two top plates. I rounded up the 2inch to 5cm.


This actually measures 209cm as the bottom and top plates don’t come to exactly 10cm. I will also be slightly short again when I add the second top plate.

How can I now add around 1.5cm to this before I rest the rafters on here?