Detached garage roof space conversion

24 Mar 2009
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United Kingdom

I have a detached new build double garage (shared between my neighbour and myself). I would like to convert my half of the roof space into storage space and fit a velux window (the wide 1140mm type).

Being a new build, the roof is made up of 10 king post trusses spaced at 600mm centres rated at 0.5 Kn/m2. The truss timbers are 84mm wide by 35mm and incredibly flimsey. There is a partition wall down the middle, this was put in after the garage had been built so doesn't quite support the trusses.

The first thing I feel I need to do is reinforce the truss beams that hold the ceiling (chords?). I'm thinking about installing 100x45 joists running from wall to wall, glueing and bolting them into each truss beam. Once that's done I should be able to board out parts of the roof area.

I'd like to know what are people thoughts and opinions on this?

Many Thanks,
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lol thanks for that insightful piece of information :p

Seriously though, reinforcing the bottom chords this way should be okay? I've checked the joist load tables and taken into consideration how much weight I will be storing (just a couple of boxes of books and junk nothing seriously heavy).

I think I may just be worrying a little too much about this first part of the project. It's the other 2 parts, fixing velux window and a door, which are the most critical where things could go seriously wrong.
Why can't you build up the central wall to meet the centre, this will halve the span, then you can attach your 4x2, bolts every 300mm no glue needed.
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Why can't you build up the central wall to meet the centre, this will halve the span, then you can attach your 4x2, bolts every 300mm no glue needed.

Yep I will be doing that as well :) The wall is only about 5mm short of the trusses so I figured I could slide some wood underneath to provide a bit of central support.

I got my 100x47 timbers today, really nice stuff 3.6m of dried C24 grade. Cost £5.50 per length which I thought was pretty good :)
I've got a few planks which are nailed across the trusses, does anyone know what their job is? There's one that is laid square down the centre across all of the bottom chords from gable to gable, another nailed to the top of all the upright chords along the ridge and 2 diagonal planks nailed to the truss rafters. To me they look like a quick and cheap way of keeping the trusses from swaying and sagging.

I'm just wondering whether I could replace some of these by doing the job properly rather than some half arsed cheap as you like job.
The planks you are seeing is probably the 4" x 1" truss bracing.

These will be diagonal, longitudinal, chevron bracings and strap noggins.

All the above are there to stiffen the roof and should not be removed.
yep 4x1, I understand that I can't just remove these things. I want to replace the one truss bracing that runs close along the centre wall with something stronger i.e. the centre wall by fixing the trusses to it and cross members between each joist/truss which will also act as strap noggins enabling me to attach the strap at each end to the new joists and noggins as opposed to just nailing the straps into the 4x1.
You can use twist ended straps. Which will sit flat against the wall, then twist 90 degs. so that they sit flat against the sides of the bottom chord of the truss.
Once you board out you will be bracing the floor considerably as well.

I assume the velux will be to bring light into the ground floor below? And not just for illumination of the storage area.
Thanks, I will look into those twist ended straps.

Yes, the velux will be letting light into the ground floor... so there will be a ~1m wide gap in the middle, essentially giving me 2 smaller roof storage spaces at either end.

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