Lintel for extension with flat roof over a patio doorway

[africadan]

I need to submit details for building control of the kind of lintel for my extension with flat roof over a 3m patio doorway

The company that produces them is called Catnic. I need some advice on what type of Catnic lintel to use with a flat roof, and I need this to look nice.

Thanks for any advice.

 

[freddiemercurystwin]

Bit more detail required: wall construction, how many courses above opening etc.

 

[africadan]

Sorry, more details:

it will be: 3000mm by 3800mm wide. Built out of brick:

Spec so far:
1. CONCRETE FOUNDATIONS: 1000 deep x 500 wide. To N.H.B.C. STANDARDS NEAR ANY TREES.
2. WALLS: 100 mm London Stock brick with 80 mm gap and 100 mm thermal block in the inside. 150 mm DPC above the ground and 16mm external waterproof render. Catnic lintels with 150mm bearing.
3. GROUND FLOOR: 100 mm concrete floor laid on 100 mm DOW FLOORMATE or similar insulation, DPM 1200 gauge lapped to DPC, on blinding and min. 100 mm hardcore.
4. NEW ROOF: JOISTS: 150 x 50 mm @ 400 centres with wall plate 100 x 50 mm, warm deck roof, and joists fixed with galvanized restraint straps at 1.5 M crs. on perimeter walls. Celotex 100mm insulation laid on 20mm plywood laid on rafters with three layers to BS747 felt above the insulation as a roof covering, with plasterboard and skim cot below the rafters.

 

[Ossy]

http://www.corusconstruction.com/en/products_and_services/building_products/catnic/

 

[freddiemercurystwin]

I take it there's at least one course of blockwork above the opening? Are the roof joists bearing on this wall above the opening or are the joists running parallel with the opening? If you click on Ossy's 'helpful' link above, open the brochure and go to page 20 you need either a CG70/100 (safe working load 26kN) if the lintels not supporting the roof or a CUB70/100 (safe working load 47kN) if it is. Probably worth checking with building control before you buy it though.

Goddamnit I've just re-read your post and you're rendering the outside, if you're worried about being able to see the leading edge of a steel lintel (understandably) forget about everything above and just use a concrete lintel inside and out and take the render back under the lintel back towards the window, fix a renderstop to the underneath and leave a gap between the stop and the frame and seal it with mastic. If you see what I mean?

 

[BuilderSte]

i would suggest using a box and lip type lintel. a concrete lintel is out the question for both internal and external as your opening is 3m wide and concrete lintels only go to 3m max. your lintel must be at least 3300mm - 3400 to get the correct bearing. provided there is around 300mm (1ft) from the underside of the lintel to the underside of your joist. (which im sure there will be) you can use a box and lip. the best way to describe it, is that the outer course is much like an angle iron and the inner is like a box section fused together. none of this lintel will be visible to you when the job is finished as the inside will b plastered and your patio doors will sit flush with your lintel, slightly recessed from the outer skin. so all should be well. ps , isnt your bricklayer/ builder able to advise you on this?

 

[freddiemercurystwin]

concrete lintels only go to 3m max.

Err, have to disagree there, http://www.naylorlintels.co.uk/properties.asp?range=HiSpec&lintel=R9&firerating=0

 

[noseall]

i think perhaps BuilderSte was thinking about standard 100x75mm concrete lintels.