roof fall on a garden room

[Jupiter01]

I am building a garden room which will be 6.5m long and 3m wide. The walls will be built from 6x2 stud walls.
I was planning to lay the roof joists along the width of this room.

Can I use 4x2's for this or does it need to be 5x2's?

Secondly, I want to have a slight fall on this roof (towards the back). I've not previously had to do a bird mouth cut and wonder if the easiest solution would be to build all the walls to be level and then fit a small wooden strip on top of the front wall - to raise this very slightly - this will then give me the fall and I could use joist hangers to fit the joists on the front and back. Could this approach work?

I'd appreciate your thoughts on this. Thanks in advance.

 

[stevie888]

You really need 5s and even C24s would be overspanned strictly by TRADA tables, but fine for a garden room.

Falls so slight wouldn't be birdsmouthed: stick your packing piece on top of your topplate and land the joists on top. 50mm will give you 1in 60 which is perfick.

 

[Jupiter01]

and even C24s would be overspanned strictly by TRADA tables

Sorry, but not sure what this means. Can you elaborate please?

Happy to use 5x2s if that's necessary. 600 or 400 centres for this?
I can use a 50mm packing piece. Do I need joist hangers or shall I just angle drill the joists?

Thanks for your help.

 

[stevie888]

Overspanned is builderspeak for a longer span than listed in the tables. These spans are determined by deflection with a massive snow load so in the real world you're fine.

I'd stick to 400crs as chances are you'll want to go on the roof once in a while and you don't want excessive deflection in the decking.

Your joists will simply sit on top of the sides with a nice overhang to keep weather of the sides. 3.6m timbers will suit nicely and dead easy to find.

 

[Jupiter01]

just one more - i assume there is no need for joist hangers? Just angle screw them?

 

[stevie888]

You mean rafter clips, but no just angled screws will do fine. We call it "tosh nailing" when using nails

 

[Jupiter01]

I don’t own a nail gun but in terms of strength (rafters and stud work) is a nail gun better than screws and an impact driver?

 

[freddiemercurystwin]

Overthinking this a bit, a few screws angle skewed into the wall plate will be fine, remember it will all be tied together when you fix the deck to the joists and the presumably you're gonna fix a member to the end of the joists behind the fascia.

 

[Jupiter01]

Overthinking this a bit, a few screws angle skewed into the wall plate will be fine, remember it will all be tied together when you fix the deck to the joists and the presumably you're gonna fix a member to the end of the joists behind the fascia.

It wasn’t just the roof joists. I was also thinking about the stud walls. Is there a case to buy a nail gun or are screws a stringer fixing? I appreciate that the nail gun will be quicker.

 

[freddiemercurystwin]

Screws will be perfectly adequate. For sure buy a nail gun if you think you'll get much use out of it long term but screws, nails, it will make no difference to what you end up with.

 

[endecotp]

Is there a case to buy a nail gun or are screws a stringer fixing?

As I understand it, people used to use nails for studwork when electric screwdrivers - or at least cordless electric screwdrivers - didn't really exist. Which isn't really that long ago in the grand scheme of things. Can you imagine screwing together a stud wall by hand!

(The history for roofs might be slightly different.)