Need advise on reinforcing my roof

[skyripper]

Bear with me, long post.

Got a new build house. As such its built to modern standards and that seems to mean "to do the job needed and nothing more". In this case, the roof space above our garage looks perfect for storage, but the builders have basically said "its sized and calculated to hold that roof and nowt else, don't stick nothing up there, it could break".

The joists are 3" x 1.5", run 230" front to back with the back resting on a wooden lintel and the front resting on a steel lintel.

These joists are part of the roof beams ( trusses in a W pattern), and support a pitched roof. The apex roof is about 72" above. There are two crossplanks at the bottom of the W pattern which I guess are for side to side movement only. They're 4" x 1". All look to be single lengths of wood, no joiners etc.

There is a column of blocks halfway down one long wall, not on the other. Its not supporting the existing joists.

Other perspectives.

Spoiler

I'd like to reinforce these so I can lay floorboards above and use the area for storing boxes etc. Couple of people have said to get some lengths of wood bolted to the long walls and run crossbeams under the joists?

Is 6" x 3" the right size for the side supports? Bigger? Smaller??
How do I fix them to the wall? Rawlbolts?
How many crossbeams should I use? 2, 3 or more?

Will this need inspecting/signoff for Buildings Regs?

Hoping to crack on with this over Easter.

 

[skyripper]

Feel my pain

 

[Maccapacca]

You could turn them all into flitch beams.

Use the same timber sections and lengths and some steel plate and bolt them, all together. By using the same bearing you'll more than double the strength. Then all you'll have to worry about is if the bearing can handle it.


http://www.urcreativespace.co.uk/our-products/structural-products/flitch-beams/

You should get all the calculations done properly, i.e. don't blame me.

 

[Craigus]

If you wanted to do it properly you may want to get a structural engineer to do some calculations, but that seems a bit excessive. Do you know any builders or carpenters who can give reliable real world advice about sizing the members?

What are the Trusses sat on where they meet the wall? Is it a wallplate? If so you could always just run joists the same direction as the bottom chord of the truss and fix them down to the wallplate. Depending on the size this could mean that the top of the new joists is higher than the bottom chord, but it is another option.

Is it a standalone garage or is it attached to a neighbours? In terms of Building Regs, I suppose strictly speaking it should be as it is a structural alteration, but in reality most people would never get this type of thing signed off.

 

[skyripper]

@Maccapacca - that isn't an option I'd heard of before. If I can make the existing joists (safely) support more weight then that is an option I didn't have before. Thank you. And no, I won't blame you.

@Craigus - The trusses are sat on a big wooden lintel at the back, and a steel lintel at the front above the garage door.

I was thinking of supporting the trusses from underneath with thicker crossbeams, but I realise I could in fact run some joists parallel with the existing trusses have them sitting on the same lintels, that are higher than the bottom chord and just board on top of those. In this way the roof trusses aren't supporting anything extra, the boards would be a mezzanine above. (amazing the words I've learned, I've never cared about words for timber in my life!)

It's an attached garage - on one side is my house, on the other side is next doors garage.

 

[lsg1r]

I'm not a builder but have worked on houses doing our extension and my dad's a builder but I'll still include the 'don't blame me' caveats.

I'd just do what maccapacca suggests but also add braces between the rafters (think of making a brick pattern from above) to reduce twist and also add slightly more rigidity.

 

[skyripper]

...I realise I could in fact run some joists parallel with the existing trusses have them sitting on the same lintels, that are higher than the bottom chord and just board on top of those...

I've come to the conclusion this is a dumb idea. The existing joists/chords/whatever are part of a big triangular truss. Which is what gives them their strength. Just running additional joists between the existing ones - they'll sag as soon as any thing is put on them unless they're a lot bigger and stronger than the existing ones.

Thinking of doing a combo of flitching the existing beams and adding either wood or steel crossbeams to support from underneath.

 

[lsg1r]

I've come to the conclusion this is a dumb idea. The existing joists/chords/whatever are part of a big triangular truss. Which is what gives them their strength. Just running additional joists between the existing ones - they'll sag as soon as any thing is put on them unless they're a lot bigger and stronger than the existing ones.

Thinking of doing a combo of flitching the existing beams and adding either wood or steel crossbeams to support from underneath.

Just do what I said about adding in braces between the beams (like a ladder), it's how your upstairs is done in most houses to stop twist and increase strength. You could also add in proper t&g flooring panels which screws in from top too if you wanted. Unless you're putting several tonnes of stuff up there I doubt you'd need extra crossbeams unless the roof trusses are like 1x1 inch.

 

[bitslice]

That pillar in the middle, you could run a couple of 1x6 from there across to the house wall, but above the existing 1x3's.
Additional 1x3's (parallel to the rest) could then be hung from metal joist supports nailed to that crossbeam. The existing 1x3's could be strapped to it as well.
They'd only be spanning half the width and could support more load.

 

[Dublove]

I wouldn't be putting *any* weight on the 3x1.5 timbers at all. They are purely to stop the roof truss spreading apart under the weight of the roof.

Your span is 5.85 meters. Thats a large span & would need big timber i.e 10 inch+

You could put new joists the other way across the width instead. 4x2 at 400mm centres with an 18mm chipboard floor would be nice and sturdy. Rawbolt a timber wall plate to the walls and use metal joist hangers to hold the new joists.

or

You could fit a steel I beam across the width (pillar to opposite wall, under the rood trusses)). Probably get away with a 127 x 76 mm I beam. Then you could use that to put 4x2 joists down the length the garage, they would notch into the I beam.

Both are going to loose you 4" of ceiling height.

I would personally go for the first option as not cost of steel beam.

P.S. If you glue & screw the chipboard floor to the joists, you will not need noggins, and it will become extremely strong.

 

[Gilly]

I would've thought an RSJ was required, but I'm no builder.

It'd give peace of mind but will cost.