Any Structural Engineers - Help re DIY Window Lintel

[davethebb]

You may have seen that I am building a 4.4 x 6.8 workshop. The walls, 2000mt high, will be 4 x 2 filled with 90 PIR & a noggin midway up between 600mm studs. The outside will be 11mm OSB, glued and screwed, and weatherboard. The Inside will probably be 9mm ply. The 45deg pitched roof will be clay tiles - approx. 3500kgs. In simple terms, the static load on the walls will be 5000kg (tiles, joists, rafters and rounding up) / 20mts (length of walls, rounding down for ease) = load 250kg/mt. I intend to install a double glazed window which will be 1800mm long and therefore my idea was to construct a lintel 300 deep from a sandwich of 2x4 timber to form the perimeter/verticals between two layers of 18mm ply - all glued and screwed together and possibly injected with PU foam to form a mini SIP. Does this sound reasonable/sensible?

 

[Jones]

If you look in part A of the building regulations online there are span tables in the appendix. The table for purlin spans should give you an idea of what's needed. Whenever I have done timber framing the drawings have always shown boards ganged on edge over openings not stacked horizontally as you are proposing, though to be fair glulam does work well. I think two 2x8 on edge should be ok but check for yourself. If you board both sides of the wall the noggins are not needed unless you want one where boards join.You will also want to double up the studs either side of the opening.

 

[Jameshow]

300mm looks a bit deep over windows I'd go for 8x2 on edge.

 

[davethebb]

If you look in part A of the building regulations online there are span tables in the appendix. The table for purlin spans should give you an idea of what's needed. Whenever I have done timber framing the drawings have always shown boards ganged on edge over openings not stacked horizontally as you are proposing, though to be fair glulam does work well. I think two 2x8 on edge should be ok but check for yourself. If you board both sides of the wall the noggins are not needed unless you want one where boards join.You will also want to double up the studs either side of the opening.

Jones, Thanks for this. The noggins are in now so I will keep them in place. The 2 x8 is a good idea and I will probably go with this although the 300mm may be reduced to 200mm - depending on the window height (can't get the original windows I planned for now....).