lean to roof

[nottsrob184]

Hi all again.
I have a question on size of roof support beams to use.
My single storey rear extension is at lintel level and i need to order the roofing timbers to support a flat tile roof.
I worked the angle of the lean to at 15 degrees and a roof timber length at 3.9Mtrs.
Does anyone know what size (thickness etc) i require. I was thinking of 8x2 's.
And anyone know if builders merchants do 4Mtr lengths.

While i'm at it it....will 6x2's be ok for the ceiling? This will be plaster boarded, skimmed and will have 6" of insulation to support over a length of about 3.7Mtrs.

 

[Deluks]

8x2's good. 4m lengths should be available off the shelf in most places.

6x2's should work, with a couple of rows of herringbone straps.

 

[hotrod]

Hi rob, strictly speaking anything greater than 10° isn't classified as a flat roof. Anyhows, 15° @ 3.9m - what centres are you using? And can you clarify if you are having a "true" flat roof (i.e. just flat roof joists), or are you having a jack rafter / ceiling joist arrangement? Where the rafters provide the fall and are braced by the ceiling joists on the horizontal? Hope that makes sense.

EDIT: Agree with Deluks if you're doing what I "think" you're doing.

 

[Deluks]

I think he meant that the tiles were flat ie: plain tiles.

I think

 

[hotrod]

I think he meant that the tiles were flat ie: plain tiles.

Of course

I think............

 

[Blagard]

I think he meant that the tiles were flat ie: plain tiles.

Of course

I think............

Plain tiles will not work at that low pitch. There are interlocking tiles that might work.

nottsrob184
Can you advise , what is the specific roof tile you are using and have you checked it is OK at 15 degrees?

 

[noseall]

Agree with Blagger, there are few choices of roof tile at 15 degree pitch.

Are you guys sure 150 x 50mm timber (for ceiling joist) is ok at 3760mm long?

 

[theoldun]

Agree with Blagger, there are few choices of roof tile at 15 degree pitch.

Are you guys sure 150 x 50mm timber (for ceiling joist) is ok at 3760mm long?

C24 50x150 maximum span 400 centres 3350

C16 50x150 ditto 3190

For 3760 you need C16 47x175
Can not give you binder sizes as do not know length of building.

Will give you roof tiles and put you wise on rafters to -morrow.
oldun

 

[nottsrob184]

Agree with Blagger, there are few choices of roof tile at 15 degree pitch.

Are you guys sure 150 x 50mm timber (for ceiling joist) is ok at 3760mm long?

C24 50x150 maximum span 400 centres 3350

C16 50x150 ditto 3190

For 3760 you need C16 47x175
Can not give you binder sizes as do not know length of building.

Will give you roof tiles and put you wise on rafters to -morrow.

Thanks all for the replies.
The existing house tiles are Flat and i was hoping to keep this style on my extension which is about 15 degress or slightly more.
I am setting the timbers at 23 bricks below existing house bedroom window angled down to the outer extension wall.
I am not sure of centres for the roof timbers but i will use 450 centres for the ceiling joists.
Hope this is a bit clearer
oldun

 

[nottsrob184]

sorry that should be 3 bricks below upper bedroom window....

 

[Static]

Hmm..
Ceiling joists spanning 3.9m at 450mm centres would need to be a minimum of 175x50 C16s maybe even 200dp if you intend to hang anything abnormal from them..

Rafters should be at same centres as the ceiling joists cos its easier.. but chances are they will need to be 200x50 C16s at 450mm centres..

Could probably get away with smaller members if you trussed the timbers up..

Would be simpler to go for a flat roof

 

[simonjay]

Hi all again.
I have a question on size of roof support beams to use.
My single storey rear extension is at lintel level and i need to order the roofing timbers to support a flat tile roof.
I worked the angle of the lean to at 15 degrees and a roof timber length at 3.9Mtrs.
Does anyone know what size (thickness etc) i require. I was thinking of 8x2 's.
And anyone know if builders merchants do 4Mtr lengths.

While i'm at it it....will 6x2's be ok for the ceiling? This will be plaster boarded, skimmed and will have 6" of insulation to support over a length of about 3.7Mtrs.

Why don't you go for a "vaulted" (although not much of a vault at 15deg !) ceiling ? In other words, the ceiling slopes with the roof ?
You can put fibreglass between the joists and a layer of celotex below (leave 50mm vent gap above insulation). Then no separate ceiling joists. Since its a lean-to no problem with the roof spreading.
I just did a 12deg roof like this using forticrete centurion tiles, or you can use redland regent at 15deg. Not plain tiles though.
You may need to beef up the rafters a bit if supporting roof and ceiling.
Simon.

 

[theoldun]

Can you give width, depth of extension, size of cavity and how many course brick from top of wall plate to underside of sill.
Can give you correct information then.
oldun

 

[nottsrob184]

Can you give width, depth of extension, size of cavity and how many course brick from top of wall plate to underside of sill.
Can give you correct information then.
oldun

It is whole width of house at 25foot and depth is about 12 foot to outer extension wall. I will go 2 bricks under bedroom window to top of proposed tiles....hope this helps.
Thanks for your help.

 

[theoldun]

Sorry, but to work your pitch out and give correct information, we need either the measure or number of brick courses from top of plate to underside of first floor window sill.
oldun