How high can I raise rafters in an A frame loft without weakening roof?

Question

I want to create standing head room in an A frame loft to make a workshop. I would need to raise the rafters to within 2 feet of the apex. What could I do to strengthen the roof structure if I do this and still leave maximum floor space? At present there are no side pieces of wood it is a simple A shape ie. an inverted V and one cross piece (rafter) at about 5 feet from the floor.

Answer 1

The pieces holding the roof up are generally called rafters. The cross pieces tying the rafters together are commonly called braces. The best solution is to install a strong and "sufficient" header beam at right angles to the rafters and above the braces so that the ends of all the roof rafters are directly resting on the header. (And in turn, the header is supported at either end - as well as in the middle if the span is greater than 10 -12 feet - by posts which in turn are supported by a load bearing wall or equivalent reinforcement directly beneath each post - on the floor below.)  Then insert shims where necessary to ensure that each rafter is positively supported by the header beam. Finally, each rafter must be attached to the header by proper sized nails or screws. Ditto for the header and the posts (again check your local building code to make sure your attachments are legal).

When you're certain that the rafters (and roof) are being properly supported by the header then simply remove all the cross bracing, box in the header and presto: you've got a lot more headroom.

(This approach assumes there is enough clearance above the braces to install the header while the braces are still in place- which also means you will have to cut a hole in the exterior wall so the header can be slid into position above the braces. If you can't do it this way, then you'll have to install temporary supports in order to remove the braces in order to install the header. If this is the case, it's no longer a simple job and you really ought to get professional assistance).

Btw, you must also make certain that the header and the support posts meet the building code for the roof load and the distance being spanned. The longer the span between support beams the stronger the header and posts must be. Good luck.

Answer 2

You will need to make sure the rafters are tied at the bottom (in your new floor and you may need to insert some purlins or double up your rafters so as to be able to raise or eliminate the collar (the thing that's in your way. There are other tricks like plywood gussets to fill in the apex but still give you headroom. Nothing a structural engineer can't sort out for you, I wouldn't think. Don't try anything without proper advice, though, as you will be in breach of Building Regs (or code, depending where you are) and could end up with a rather nasty happening. Bear in mind that the floor structure may need additional strengthening especially if you have a lot of heavy kit (benches, machinery) up there. My workshop is in a cellar and the head room is a scant 1800mm  which is fine if I don't jump up and down too much.

Answer 3

Hi

I think you've got your terminology a bit wrong.

As Mr Peabody says the rafters are the structures that hold the tiles, so I'm not quite understanding what you want to do.

The bits that form the ceiling of the room below and the floor of the loft are the joists and if you want to make a workshop in the loft these will need to be reinforced or replaced with larger ones. If it's just a piece of wood mid way up in the loft that ties the rafters together, this could possibly be moved up a bit but as a rule of thumb never more than two thirds up. It is possible to make a frame to hold the rafters ............... best get a structural engineer to have a look. It sounds very complicated