Porch Rafters / Sundeck

[Barewolf]

Hi

I am wanting to build a Decking area outside my back door, and I want to go a little further and build a porch with a roof over the decking area that will be weatherproof.

My Idea (See Pic) would consist of 3" x 3" Wall Plates / Posts which I will attach to the brickwork using 12mm Anchor bolts.

when I was thinking of the roof, I was wondering if 4" x 2" Rafters would be enough? Theres not going to be any heavy duty tiles on the roof, I'm thinking of just using plastic sheets similar to what you use for greenhouses.

The area would be 6ft out from the wall, x 10ft, possibly 8ft.

[Taf]

It's not weight of a roof that you have to only worry about, but wind loading. The structure has to be able to hold down what would effectively be a large kite.

I fancied something like that, but opted for a simpler option...a sun sail anchored in 2 points to the house, one to a solid wall and one to a brick shed. Easy to put up, easy to take down, solid against the weather, and only a little rain gets through. And they last for years.

[martyh]

The size of rafter as a minimum spec will be ok ,just make sure that the plastic (not sure what you mean by that,got a pic?) is securely fixed or it will end up the other side of worcester as taf said

[Barewolf]

this is what i mean

http://www.diy.com/diy/jsp/bq/nav.js...&isSearch=true


They have the special rails so they slide in and fit similar to a greenhouse, i think they are quite tough, ive seen pergolas with this fitted that are sold by manufacturers.

[martyh]

Originally Posted by Barewolf

this is what i mean

http://www.diy.com/diy/jsp/bq/nav.js...&isSearch=true


They have the special rails so they slide in and fit similar to a greenhouse, i think they are quite tough, ive seen pergolas with this fitted that are sold by manufacturers.

Yep ,polycarbonate roof sheets ,should be fine and weigh next to nothing

4x2 timbers will be fine as long as they are anchored securely

[Barewolf]

i was going to use a bird mouth cut for the rafters, so in theory i wouldnt need to anchor those rafters would i? arent you supposed to use joist hangers or something similar?

Joist hangers would only be good for a straight horizontal joist or rafter, but im sure theres something similar to fix in place sloping rafters.

[martyh]

Originally Posted by Barewolf

i was going to use a bird mouth cut for the rafters, so in theory i wouldnt need to anchor those rafters would i? arent you supposed to use joist hangers or something similar?

Joist hangers would only be good for a straight horizontal joist or rafter, but im sure theres something similar to fix in place sloping rafters.

A birds mouth is the correct way to seat the rafter onto a beam but it will still need to be fixed either by screwing through the top or as you say using a joist hanger ,either is acceptable ,personally i would favour a joist hanger fixed horizontally on the eave beam with the short 90 degree bend facing out towards the garden ,this will stop any "racking"of the framework .Obviously you would need to set the hanger at the bottom of the eave so the 90 degree bend doesn't protrude above the rafter due to the pitch of the roof

[Barewolf]

Id prefer that too martyh, but all the joist hangers ive seen are 90 degrees so the roof would have to be straight to use them, unless they make joist hangers that have a set angle so it can be screwed to the wall plate and the rafter can be angeld at a degree, Ie; 60.

[martyh]

Originally Posted by Barewolf

Id prefer that too martyh, but all the joist hangers ive seen are 90 degrees so the roof would have to be straight to use them, unless they make joist hangers that have a set angle so it can be screwed to the wall plate and the rafter can be angeld at a degree, Ie; 60.

If you set the long part of the hanger along the eave beam horizontally with the short 90 degree part facing out into the garden it will work as the eave and the rafter will be at 90 degrees to each other ,joist hangers don't have to be used vertically

[Barewolf]

Originally Posted by martyh

If you set the long part of the hanger along the eave beam horizontally with the short 90 degree part facing out into the garden it will work as the eave and the rafter will be at 90 degrees to each other ,joist hangers don't have to be used vertically

Is this what you mean? (See Diag)

Basically, an Upside down hanger?

[martyh]

there i've drawn a white line to represent the hanger on your existing design

[Barewolf]

i see what you mean now, i was hoping to find a pre angled joist hanger that was set at maybe 60 deg, but i guess they dont make them, so i will have to cut the wood to fit the wall plate.

[martyh]

Originally Posted by Barewolf

i see what you mean now, i was hoping to find a pre angled joist hanger that was set at maybe 60 deg, but i guess they dont make them, so i will have to cut the wood to fit the wall plate.

you can get flexible hangers ,basically just tin plate ,but they will not stop the racking of the framework .should point out that technically the name is joist strap not hanger

these are hangers you could use these at the ridge end

these are straps you need these at the eave end ,they are rigid steel and will stop any racking and hold the joist in place in high winds they are available from any builders merchant at a variety of lengths

---------- Post added at 21:54 ---------- Previous post was at 21:48 ----------

just to be clear because i edited my last post ,joist hangers are flexible and can be used with any angle

joist straps are rigid and bent at 90 degrees

hope this helps

[Barewolf]

would these be better than straps?

http://www.toolstation.com/shop/Stru.../sd3224/p69625

[martyh]

Originally Posted by Barewolf

would these be better than straps?

http://www.toolstation.com/shop/Stru.../sd3224/p69625

a little small .in high winds they would have the potential to rip out of the wood because of the lever action from the joists .Assuming your rafters are spaced at 450mm then a strap of about 300mm on the long length would be better