storage space in garage roof

[swordfish]

I'm running out of space in my 18'x8' single garage an have realised that there's a possible "loft" space above the door end of the garage.

The single garage is part if the house, but pokes out about 8' proud of the upstairs level. This part has a pitched roof with concrete tiles. The ceiling is plaster boarded and looking above the boards the tiled roof is held up by 4" x 2" triangular site built (rather than manufactured) trusses.

The wall above the door is held up with a box section RSJ - the same supports the front wall of the first floor above the middle of the garage.

What I'm hoping to do is to remove 3' pieces from the centre of each of the horizontal rafter section of each of the trusses, re-bracing them using shorter 4"x2" horizontal "mini-rafters" further up towards the ridge. I'll then attach the cut ends of all the existing rafters to the longer sides of a rectangular 4"x2" frame that will be supported at both short ends by attachment to the RSJs. This rectangular space will house a fabricated ladded, that will pivot/swing down to provide access.

The obvious question is will the roof stay up!! Would I need to put in any additional bracing. I'm thinking of various bracing options: doubling up on the mini rafters, ie one each side of the existing trusses; vertical from the cut ends of the rafters upwards; diagonal from the cut ends to the sloping members of the trusses; or doubling up on the longer sides of the rectangular frame so that they are 4"x4" (or even 6x6?).

Any thoughts/suggestions would be appreciated.

RSVP

 

[chingerspy]

Swordfish good luck with the loft. I'm no experienced structual engineer so will refrain from advising you.

I did the same a few months back though and it's amazing how much storage space it creates. Mine was a single garage fully built into the house with concrete and breeze block walls either side. The area created was about L8'xW5'xH1.5'. I got away with angle grinding slits for joist hangers and then some 2x6's and 2x4's C16 across with noggins to create the framework. One half has 18mm ply over it (because I'm cheap and nothing falls through the other side

Works really well, I have all my fishing gear and a few other deep storage items up there too.

 

[Lons]

The obvious question is will the roof stay up!! Would I need to put in any additional bracing. I'm thinking of various bracing options: doubling up on the mini rafters, ie one each side of the existing trusses; vertical from the cut ends of the rafters upwards; diagonal from the cut ends to the sloping members of the trusses; or doubling up on the longer sides of the rectangular frame so that they are 4"x4" (or even 6x6?).

Any thoughts/suggestions would be appreciated.

RSVP

My advice would be don't undertake this before you've done the calcs or consulted someone else to do them for you. Don't want to put you off - just do your research properly first.


Standard concrete tiles will weigh at least 50kg per sq mtr without the weights of felt, laths and the woodwork itself etc. so your trusses are likely holding up a couple of tonnes !!!!
Don't want that falling on your head (or machinery ) and the local building control officer would take a dim view as would your mortgage / insurance provider if applicable, as it is a structural alteration.

Roof design and structure are very much a part of building regulation control and the guys would be happy to advise. be aware if you do consult them though you can't then risk a bodge job - sure you wouldn't do that anyway.


Bob

 

[trousers]

You don't say what the roof pitch is.
If it is 45 deg then your head room would be approx 4 ft.
If as low as 30 deg then headroom only approx 2 1/2 ft.

Also taking 3 ft out of an 8 ft span only leaves approx 2 1/2 ft useable level space each side of your opening, with diminishing useable space as calculated above. Putting collars across each pair of rafters at a higher level will also impinge on the useable space.

Doubling up the rafters will do little to strengthen the roof if you are going to cut away the ceiling joists. These ceiling joists are preventing the roof from failing by spreading outwards (doing the splits), and it is these joists which need replacing with the collars at a higher level. The trouble is that the higher you put them, the less effective they are, and they may not be an adequate substitution without resorting to measures such as plywood flanges.

Check your measurements, and ask yourself if its really going to be worth considering. And as Lons has said, it is a structural alteration which comes under Building Regs, and they would want to see calculations. And so would your prospective purchaser if you ever came to sell the property later on.

Is it really worth the effort?

 

[swordfish]

Hi Guys

Thanks for your very helpful comments. I must say that I'd not realised how heavy the roof would be!! Or that building regs would be needed!!!!

The main reason for cutting the rafters was to be able to have a ladded hinging down in the centre of the roof between my existing benches. Not having the sections of rafter would have meant that the ladder virtually disappearing into the ceiling.

Time for a re-think. Plan B looks like replacing the plaster board with ply screwed to the underside of the rafters - which would potentially give me an extra 4"-5" of space compared with boarding above the rafters. It's mainly to store boxes so these will fit between the rafters. A non-fixed ladded is likely to be able to be stored at ceiling level (up and over door permitting) and would give better access to the various sections anyway.

Many thanks for your helpful advice.