Flat roof support above patio door with side panels

[ANGLER]

converting my old lean too conservatory to a flat roof construction.

We are going to have new French door with side panels Height: 2090mm
Width: 2390mm. My question is what sort of roof support is required above the doors? Roof height is an issue with the house roof wall plate.

 

[noseall]

Use either a laminate timber beam or a steel lintel.

Any lintel arrangement above a 2.4m opening is likely to exceed 6" in depth no matter what.

I suppose something like a 152mm x 89mm with holes in the flange to take a plate bolted to the top or a pair of 200mm x 50mm timbers bolted together may do.

Either way you will end up with at least 200mm above the doors.

 

[noseall]

....or, i guess if you fitted an 'I' beam and bolted a timber sandwich into the web either side, you could then fix the roof timbers at beam level - using the one web timber (internal) to carry the hangers and roof joists and t'uther web timber (external) to deal with the fascia.

And the same arrangement would work with a timber laminate beam, i.e. fixing the roof joists (and hangers) to the face of the beam rather than on top.

 

[ANGLER]

lean too

• ANGLER
• 22 Sep 2011
• 3

I think the doubled up 200x50mm timbers may be best suited. I don't want to disturb both adjoining walls. Pic shows the existing door opening, this opening will be increased to the desired width. length of a building block will be left on both sides.

 

[browfish]

I rang up catnic and they told me what lintels i needed. I was just going to buy and extra stong lintel that came in spans for my 4m opening however they advise me that i needed 2 separate lintels for the cavity wall due to the fact i was planning on having top hung bifold doors. Might be worth asking as it was free advice over the phone. My building inspector was then happy with what they suggested without needing calcs

 

[ANGLER]

Doubled up 200x50, I beam sandwich or laminate beam. What is a laminate beam, and now totally stumped which one to use. Decision time.

 

[tony1851]

What is the span of your new flat roof? (ie distance between existing house wall and new wall where the doors will be).

 

[ANGLER]

Existing flat roof 2400mm. New roof 3700mm

 

[tony1851]

If the new flat roof spans 3.7m. on to the beam over the doors, then two 50 x 200 firmly bolted together will be fine.
Your main problem will be arranging for ventilation above the insulation (unless you are having a warm roof deck). If the insulation is going between the joists, the tops of the joists will need to be above the top of the beam by about 2" to allow air flow between the insulation and deck.
Ideally you would run the roof joists over the top of the beam, but presumably this would give you a problem with roof height?

 

[ANGLER]

Thanks for the info. 200mm would prevent me having a adequate ventilation gap. Would you recommend 152x89 UB I beam with sandwiched between timbers. If so could I use a smaller beam and how would I attach to the walls on both sides, without making a hole on each sides.

 

[tony1851]

The 152 x 89 will be OK structurally, but may bend just a little under maximum load (eg heavy snow). Leave a little extra clearance over the frame to allow for this (5 -10 mm?)
Ideally the beam should sit on a padstone in a socket in the wall, but if you can't do this, you could use a heavy-duty joist hanger. Google 'Simpson JHM/HJHM' and there are some diagrams of the hangers with safe-load tables.
You may need to be prepard to work out some loads if your building inspector asks for justification. Presumably the hanger will be over the lintel over your existing window; you may need to check that this will still be adequate.

 

[ANGLER]

If I use the 2 x 200x50mm timber method, what type of bolt/washers shall I use?

 

[tony1851]

Go to B&Q and get a 3ft length of 1/2" threaded bar, plus a pack of 10 1/2" nuts and 10 flat washers. Cut the bar into five 6" + lengths with a hacksaw. Clamp the 2 timbers together and drill the 5 equally-spaced holes along the centre with a wood cutter of slightly larger diameter. The pieces of cut bar are passed through, and secured by tightening the nuts/washers on both sides. Make sure at least one thread protrudes from the nut.
On the room side of the beam, where you may not want the nuts sticking out, consider countersinking the nuts/washers. You will need a larger bit to accomodate the width of the nut/washer, and also a socket to tighten them up.

 

[noseall]

TOP TIP

Before cutting the threaded bar wind a pair of nuts onto the bar and keep winding them until you reach the point where you want to cut.

Have one nut one side of the cut and the other nut on t'uther side.

Then cut between the nuts. Round the burr ends of the bar with a file or grinder. Then slowly wind the nuts of the bar and these will re-cut the thread for you.

 

[ANGLER]

Just asked my local timber merchant for a quote 200x50mm timber joists. They quoted back C16 reg'd and graded carcassing 44 x 195. Would this reduced size ok for roof joists. If not what grade