Hello all,

I have a trussed roof in my garage so cannot put anything weighty up there without doing something so.

Adding joists:
Using joist hangers place load bearing joists directly underneath the trusses?
Using joist hangers place load bearing joist at 90 degrees to the trusses (cross cross)?
Place the load bearing joists alongside the trusses, effectively raising the floor level a couple of inches, making this a separate structure?
Place the load bearing joists as above but also bolt to the trusses?

Trusses are 4" x 1"
My new joists are 6" x 2"

Will not be putting lots of weight up there BTW but it all adds up.

Span is 5 meters.

Cheers Mark

6x3 at 16" spacing was what we used in the last garage which had a walk on floor.

We also didn't use hangers we sat it on the wall plate.

It was done by a surveyor n builder.

Old dimension of garage 5m x 6.5

New one is a little better. 4.8 x 8.5 :-)

I'd favour sitting the new joists on the walls and alongside the trusses, bolted to the trusses for good measure. Seems the simplest way and ensures the load is kept separate from the trusses themselves.

Erm, bolting the joists to the trusses will ensure the trusses DO pick up the floor load! A truss is a much stiffer structure than a simple joist, so it will attract the loading.

What centres are the trusses at?

If you want a proper floor up there, suggest you install the joists at 600 centres maximum, such that the top of the joists is about 15 - 20mm higher than the top of the truss bottom chords. Then floorboard around the truss web members so the two systems are not actually connected. The 15mm gap will ensure that as the floor deflects under load the trusses won't pick up any significant inadvertent loading.

Cheers R

[Edited on 8/2/13 by rachaeljf]

600mm between centres, so alongside is looking best then, my new joists will then be proud by a couple of inches and will not affect the integrity of the trussed roof

It's not to take any real load, but as time rolls on and you collect junk the weight creeps up.

Thanks Mark

5meters is quite a long span.

Have you checked the building regulations document?
www.tameside.gov.uk/buildingcontrol/guidancenotes/note7.pdf

Not that these rules necessarily apply, but its the same laws of physics!

Matt

It depends on what you are loading the trusses with.

Most trussed roofs are designed to accommodate a cold water storage tank so if you are just using the area for storage the load is not the issue, only how you spread the load. i.e. the trusses will take quite a substantial extra load as long as it is spread evenly.

So it would not do any harm in this case to bolt strengthening joists to the existing truss.

IMHO of course

In reality I'm living in the 7th (and last!) house I've built. The garage trusses are directly floored with chipboard and its filled to the apex with car stuff. Been there 15 years and not a suggestion of movement. Span is 6m plasterboard ceiling and welsh slates on sarking so it was well loaded to start with.

Living in is a different matter though

Cheers!

It's garage roof, attached to the house, big heavy Marley tiles on top.

If I walk about on the trusses no sign of movement or deflection, I would just rather spend £200 making it more secure

quote:

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Originally posted by rachaeljf
Erm, bolting the joists to the trusses will ensure the trusses DO pick up the floor load! A truss is a much stiffer structure than a simple joist, so it will attract the loading.

What centres are the trusses at?

If you want a proper floor up there, suggest you install the joists at 600 centres maximum, such that the top of the joists is about 15 - 20mm higher than the top of the truss bottom chords. Then floorboard around the truss web members so the two systems are not actually connected. The 15mm gap will ensure that as the floor deflects under load the trusses won't pick up any significant inadvertant loading.

Cheers R

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You won't get anywhere near complying with building regs/BS 8103 with those joists on a 5m span. However, they will be adequate for light storage in the constricted roof space of a typical garage. The building regs are more concerned about the bounciness and deflection (known as "serviceability" ) of a floor rather than its ultimate capacity.

Roof trusses are normally designed for a nominal maintenance load so yes there probably is some spare capacity in them. If Mark uses the 6x2 joists as I suggested, then any overloading distress in the new floor is readily seen from below by observing the amount of floor sag against the (straightish) line of the truss chords.

Cheers R

[Edited on 8/2/13 by rachaeljf]

quote:

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Originally posted by matt_gsxr
5meters is quite a long span.

Have you checked the building regulations document?
www.tameside.gov.uk/buildingcontrol/guidancenotes/note7.pdf

Not that these rules necessarily apply, but its the same laws of physics!

Matt

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The advantage of placing the joists alongside the existing ones is that I do not compromise the building as I have not touched the existing structure.

Although the span is 5m today I need to modify my utility room which encroaches upon the garage space, today it's a large box at one end, I will reduce its width and grow its length this year so the span will reduce to 4m.

The purpose of this is not to make a room, merely to take useful bits off the garage floor and shove them in the loft space, stuff you rarely touch, spare sets of wheels etc, I guess most people would not even bother doing this TBH, just board and spread weight evenly, heavy stuff to the Eve's but for £200 I would rather be safe.