25 gallon tank, 2x4 joists

Grenage · 1 May 2021

I'm going to join a 25 gallon tank to our existing 25 to accommodate our power shower.

The roof members are approx 50 x 100 with ~400 centres across 4m. I don't have a supporting wall.

The existing tank is sitting on ply, resting on 2x4 across the joists. I assume it would be alright to do the same across unloaded adjacent joists? I had a look at TRADA tables but I couldn't make much sense of it.

oldbutnotdead · 1 May 2021

You'll need a decent loadspreader. 25 gallons is about 110 litres so call it 120kg with the tank weight. Put it on a square metre of ply on adjacent joists as near to supported ends as you can get & you should be ok.
4 x 2 are rated for floor span of about 1800mm. If your house is old (pre 1920 or so) your timbers, if in good condition, will be much stronger than modern stuff (much finer grain).

Grenage · 1 May 2021

Champion, thank you. The house is 1905, so that's encouraging.

Tigercubrider · 1 May 2021

Do the tanks need to be next to each other? Or could a connecting pipe be say, a metre long ?(supported)
Just thinking that you might have an upstairs wall that could provide additional support?

oldbutnotdead · 1 May 2021

If you want to be paranoid/informed, you could run a test- measure from ceiling to floor below now, stick some weight on a spreader in the tank position and remeasure. Upy to 5mm, don't worry. More than that and/or any nasty cracking noises maybe time to sister some 6 x 2 into the loaded area

Grenage · 1 May 2021

Hi, Tigercubrider. Unfortunately there's a stud wall to divide the loft roughly over the wall. It looks like a large tank was there at some point and it went a bit wrong. They've cut out the member and joined up with replacement wood.

Oldbutnotdead. Good idea, thank you. I shall do that.

Grenage · 3 May 2021

Went in with no dramas, although moving the feed took all day. Cheers for your advice!

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25 gallon tank, 2x4 joists

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