Joists for Storage in Existing Garage

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Hello,

I have a detached single skin brick garage (with two brick piers on each length of wall) built in 1961.

Span 8'10"
Wooden Wall Plate Width 3" (sits on top of the single skin brick wall).
Rafters spaced at 17".
Existing Rafter Ties are approx 3"x2" timber spaced at 5.5' intervals.

I'd like to create some joists so I can store more stuff in the roof void. I'm not planning to board it over as I appreciate this will add a lot of weight.

I was considering C16 timber, either 4"x2" or 5"x2" (metric equivalents) to span the 8'10" at 17" intervals to match the rafter spacing. I would rest these on the existing 3" wide wall plates with ends angled to match roof line (provided I can manoeuvre them into place) and nail or screw sideways into the existing rafters so they act as rafter ties as well as joists for storage. I'd leave the existing timbers in place, and simply put the new joist/tie on the opposite side of the rafter in those instances.

Any tips or advice much appreciated. Especially with regards to which wood type and dimensions to use, whether to screw or nail into rafters, and whether I am likely to be able to manoeuvre them into place in one piece? Thanks

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4x2 c16 fixed to each rafter. You will strengthen it considerably if you fit noggins at 1/3 of the span and board it
 
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4x2 c16 fixed to each rafter. You will strengthen it considerably if you fit noggins at 1/3 of the span and board it

Hi, thanks for the advice, so do you mean essentially fit 2 noggins over the span, approx 3' feet across from each wall plate?

Would you advise nails or screws to attach to rafters. I heard that nails are often preferred as they can cope with slight movement without snapping?

Finally, would 4x2 support boarding, if so what type/thickness of boards do you recommend?

Thank
Kevin
 
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Wiggling them in will be the problem. You need to do some sums....
Length of new joists = 8'10 + 6" so 9'4
Clearance between walls 8'10
Wiggle room 1'5 minus thickness of new joist so 1'3
Pythagorus says you end up with just over 8'11" to play with....
 
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Nail or screws what ever is easiest. It's really for fixing an not performing an structural function.

Yes 3' or so in from each end for noggins

600mm joist spacings normally need a 22mm board - normal chipboard flooring or loft boarding, but as its just storage then 18mm would do.
 
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Consider (if you can't get the joists in) using some lightweight truss clips or mini joist hangers nailed to wall plate with sheradised twist nails - you won't have enough depth to nail all the holes but it won't matter.
 
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Wiggling them in will be the problem. You need to do some sums....
Length of new joists = 8'10 + 6" so 9'4
Clearance between walls 8'10
Wiggle room 1'5 minus thickness of new joist so 1'3
Pythagorus says you end up with just over 8'11" to play with....

Cheers for the advice :) Yes, I am worried about this. I was thinking I could get one end in over the 3" wall plate first then manouvre the other end in place, but it will be tight. The bricks are 4" wide so effectively have a spare inch each side beyond the wall plate.

Consider (if you can't get the joists in) using some lightweight truss clips or mini joist hangers nailed to wall plate with sheradised twist nails - you won't have enough depth to nail all the holes but it won't matter.

Thanks for your advice :) ould screws be better, I'd rather not use nails as I find it might cause cracks etc?

Finally, is 4x2 sufficient?
 
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Think your wiggle won't work- or will need you to shorten the joists by an inch. You'll still only have 9'3" to play with...
4 x 2 will be ok for storing bits of timber, ladders, that sort of stuff but wouldn't be putting bags of cement up there...
 
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4 x 2 will be ok for storing bits of timber, ladders, that sort of stuff but wouldn't be putting bags of cement up there...
Have you seen the amount of crap in a loft of the average semi with 3x2 ceiling joists? I've seen offices and bedrooms. o_O

The concept of noggins and boards massively increases the capacity of a floor by way of load sharing and rigidity. As will reducing the spacing to 400 or 450mm
 
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Think your wiggle won't work- or will need you to shorten the joists by an inch. You'll still only have 9'3" to play with...
4 x 2 will be ok for storing bits of timber, ladders, that sort of stuff but wouldn't be putting bags of cement up there...

Cheers chaps.

I'll buy some treated C16 or CLS timber. I assume if I can only overhang the wall plates 2" each side that will suffice as that may be the case in order to wriggle the joists into position. Also wondering whether treated 89mmx38mm CLS would do the trick? It's a lot cheaper

Thanks
 
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Think your wiggle won't work- or will need you to shorten the joists by an inch. You'll still only have 9'3" to play with...
4 x 2 will be ok for storing bits of timber, ladders, that sort of stuff but wouldn't be putting bags of cement up there...

Does this calc look right based on an aerial view of garag
SCAN5973.JPG
e?
 
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You've given yourself too much gap between rafters, you have to allow for the thickness of your new joists (so useful clearance will be 370mm not 430)
 
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