Hi

I've been asked to build a 15' x 12' wooden deck to hold a hot tub. Most of
the joists can rest on a small retaining wall, a concrete slab and a wall
plate fixed to the garage wall.

The tub holds 1300 + litres of water & up to 6 adults, so adding the (as yet
unknown) weight of the tub itself I could be looking at 2 tonnes here.

Would I increase the strength much by spacing the joists at 12" rather than
16" or would extra noggins be a better bet?

Cost isn't the major issue, I just want to make sure it's strong enough.


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257

The Medway Handyman wrote:
Hi

I've been asked to build a 15' x 12' wooden deck to hold a hot tub. Most of
the joists can rest on a small retaining wall, a concrete slab and a wall
plate fixed to the garage wall.

The tub holds 1300 + litres of water & up to 6 adults, so adding the (as yet
unknown) weight of the tub itself I could be looking at 2 tonnes here.

Would I increase the strength much by spacing the joists at 12" rather than
16" or would extra noggins be a better bet?

Cost isn't the major issue, I just want to make sure it's strong enough.


--
Dave
The Medway Handyman


will the footing for the retaining wall take the extra weight? it would
be like parking a couple of cars on it !!
www.medwayhandyman.co.uk
01634 717930
07850 597257

"The Medway Handyman" wrote in message
news
Hi

I've been asked to build a 15' x 12' wooden deck to hold a hot tub. Most
of
the joists can rest on a small retaining wall, a concrete slab and a wall
plate fixed to the garage wall.

The tub holds 1300 + litres of water & up to 6 adults, so adding the (as
yet
unknown) weight of the tub itself I could be looking at 2 tonnes here.

Would I increase the strength much by spacing the joists at 12" rather
than
16" or would extra noggins be a better bet?

Cost isn't the major issue, I just want to make sure it's strong enough.


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257



I'd definately over engineer. 8" timbers, 12" centres and lots of
intermediate supports along the length. Noggins will just prevent twisting.
Running the joists the shortest distance (12') I'd go with a 3' span max. I
assume than means the joists underneath the tub would be supported in at
least 2 places.

I base this purely on experience with a neighbours tub and no scientific
reasoning!

The Medway Handyman wrote:
Hi

I've been asked to build a 15' x 12' wooden deck to hold a hot tub. Most of
the joists can rest on a small retaining wall, a concrete slab and a wall
plate fixed to the garage wall.

The tub holds 1300 + litres of water & up to 6 adults, so adding the (as yet
unknown) weight of the tub itself I could be looking at 2 tonnes here.

Would I increase the strength much by spacing the joists at 12" rather than
16" or would extra noggins be a better bet?

Cost isn't the major issue, I just want to make sure it's strong enough.


Online calculators should help. A quick look turns up
http://www.awc.org/calculators/span/...rcalcstyle.asp - it's
american so not ideal, but suggests that 2 x 10 softwood joists at 16"
centres can span 11'6" with a 2 tonne dead load. Playing about with the
options should give you a good guide.

Andrew

wrote:
The Medway Handyman wrote:
Hi

I've been asked to build a 15' x 12' wooden deck to hold a hot tub. Most of
the joists can rest on a small retaining wall, a concrete slab and a wall
plate fixed to the garage wall.

The tub holds 1300 + litres of water & up to 6 adults, so adding the (as yet
unknown) weight of the tub itself I could be looking at 2 tonnes here.

Would I increase the strength much by spacing the joists at 12" rather than
16" or would extra noggins be a better bet?

Cost isn't the major issue, I just want to make sure it's strong enough.


Online calculators should help. A quick look turns up
http://www.awc.org/calculators/span/...rcalcstyle.asp - it's
american so not ideal, but suggests that 2 x 10 softwood joists at 16"
centres can span 11'6" with a 2 tonne dead load. Playing about with the
options should give you a good guide.

Andrew

I'll add my 2d worth...strength is less an issue than flexure. Make a
truss, or use a really well screwed down stressed skin of marine ply to
stop things wobbling. In fact i'd do both. Mock it up small scale with
balsa CA glue and so on, and push it every which way to see how it
bends. Then add struts and plates till it stops.

Then copy that.