My daughter has asked me if I could enlarge the loft hatch in her top floor flat as the existing one is only 23" square and very difficult to get through once the ladder is in place.

Over the weekend I had a look but the roof is supported with pre-fabricated roof trussees at something like 24" centres which is why the existing hatch is so small.

I can't make it longer in the same direction as the trusses because the hatch is in a narrow hallway so to do anything I would have to cut away a section of one of the trusses.

In a conventional roof I'd be happy to do this and then trim between the adjacent ceiling joists but I'm a bit nervouse of these pre-fabricated trusses.

Is it possible / safe to cut a section out of one and then trim between the two trusses either side to put back some support?

The section to be removed is only the ceiling support timber (ie it would not involve any of the vertical members).

Any advice would be appreciated.

John.

Yes - it can be done - my loft hatch spans 2 gaps, with the middle beam cut. There are 2 cross-pieces to brace the uncut beams and hold up the ends of the cut one.

All parts of a pre-fab roof truss do something and none should be cut away.The ceiling joists are under tension and tie the foot ends of the rafter section.

quote:

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Originally posted by wicket
All parts of a pre-fab roof truss do something and none should be cut away.The ceiling joists are under tension and tie the foot ends of the rafter section.

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If removing a section of just a single pre-fab truss puts the structure at any risk whatsoever, I'll eat my hat. 'Safety factor' and 'huge' spring to mind.



EDITED TO ADD: Liam takes no responsibility for any loss, injury or death resulting from collapsing structures caused by...

In all seriousness try asking in the building section of DIYnot.com. Useful mixture of time-served builders, structural engineers, cowboys, armchair laywers, keyboard warriors...

[Edited on 16/3/10 by Liam]

Hmm.. I agree with the warning about pre-built roof trusses bit.

I would be VERY careful about cutting them.
The downside is the roof could collapse, as a worst case.

Also consider a gale blowing and moving that part of the roof or taking it off.

The really BAD part is when your insurance company wont pay out as You weakened the roof. It's a bit like car insurance claims!

Any Insurance Co will check to see the claim is valid, and take into account any factors that would reduce their payout.

So what ever you do, do it correctly, as roofs are expensive to replace.

Just my 2d's worth.

whilst it galls me to say this .......

could you pay someone with liability insurance in to make the change. If it goes wrong then you can get their insurance to pay out.

Tell her she's luck - my loft access is 13"*23"

Hugh

Tell her she's luck - my loft access is 13"*23"

Hugh

It'll be fine if it's one truss - I did it in my last house. Make up and bolt in the box sections first (which will define your loft hatch and provide strength between the next two trusses) then start cutting. Cut halfway through the beam and leave it a while. If you come back and the saw is clamped tight in the beam or the saw has fallen out becasuse the gap has widened, stop and repair! If not it will be fine. I also used that method when I installed a velux - just watch the saw cut!

[Edited on 16/3/10 by contaminated]

If it was my loft I'd get a builder in - I'm not that brave!

That's how I got my nice wide hatch, with ladder...