Hi all. I hope you are well. This is my first time here so please point me in the right direction if this is not the correct place to post. I would like to install a 300 litre unvented cylinder in my loft (I'm a plumber) but need to figure out how to make the platform to support it. I live I a Bungalow from the 1930's which has 100 x 50mm joists at 400mm centres. The span from binder to load bearing wall is 1.9 metres and then from binder to wall plate 1.5 metres. The dead load of my tank I believe is 1400 kn over an area of 0.28m2. Would I be able to span a few joists with larger timbers/ double up the joists etc? Any advice given I will gladly take. Regards Lee
Unvented cylinder around 350kg (777lbs) full, with my rough sums,might vary abit depending on make of cylinder.
350Kg is quite a weight, I've got a 70 gallon tank in the loft with a similar construction, it actually holds nearer 55 gallons which is about 250Kg. There is a big structural timber right underneath it and its right next to the gable wall too where this timber is supported, I wouldn't want to put 350Kg just on joists even if they're sistered up or load spread. You're looking at the weight of 5 people. Ideally you want something solid underneath it or have it as near as possible to something solid like an outside wall. Is it an option to add height to the 2x4s and screw/glue another 2x 4 timber on top? Doubling the height of the timbers increases the stength 8 fold. If not, perhaps look at screwing in long steel plates to the joists, screwing 25mm ply across many joists etc.
Hi, thanks for the reply. Unfortunately I cannot get it to be close to an outside wall due to it's height. I can span 2 brick walls of a room below which is a 2.4 metre span. In the opposite direction of the joists. The tank would probably be in the centre of this span though.
Sorry all. I was meant to say 14kn m2. I will have 3 showers running at the same time with 18 litres of flow per shower so need the big tank. Thanks for the replies
What about using a slimline unvented cylinder on ground floor somewhere, Megaflo,Gledhill,Vaillant, etc all do them.
350 kg centrally located on a 2.4m span, 2nr 200 x 50 joists should suffice. Get 3 mates to stand on 1 joist and see if that supports them.
Done a calc (to involved to put on here) but one SC24 50x200 joist would be man enough giving a 5mm deflection so 2 joists would eat it.
So here is my set up at home. Hope it makes sense Oh wow, thank you so much. Is this spanning the 2.4 metre walls then and then plywood on top. I don't mean to be rude but would it be possible to lower the height and use a thicker timber as I need to keep as much height as possible due to the cylinder being 2 metres high. Again, thank you for your time spent helping out.
You could use 2 smaller unvented cylinders to achieve same storage. That would let you put the higher base and spread the weight greatly. They would need piped together in a simple arrangement. Also have the loft roof (between rafters) insulated around the cylinder and ideally the entire roof
4nr C24 47 X 97 would do the job, deflection would be 7.7mm but as with all things structural this will be erring on the safe side. Calculations based on 350kg load and effective span of 2.5m i.e. actual span plus 100mm bearing either side, all in accordance with BS5268-2:2002. You could have even lesser depth joists but obviously the number would increase, I think 4nr is the optimum solution.
No way. Thank you so much. I had an engineer in and he said the same. Recommend though to put 50 x 150 x 3 across the span. Will show the calcs later once I have learnt how to reduce the size of the image
Yep, 150 deep also works and stresses in wood are less, but to be expected as joists contain 64% more wood. Also contain more wood than original suggestion of 2nr 50 x 200 joists. More than one way to skin a rabbit but depends how much head room you are trying to save?
Thanks again for your help. Really is good to have a second opinion. In your scenario, is this just going off the top of the existing joists at this span or onto the walls? If I did go with the lower height joists as you and the engineer said is a possibility, would doubling up 3 be ok? It seems like it would. Thank you again kind sir for your help.
Over the years,have fitted many water tanks & cylinders in lofts Usually it was the idea to install suitable-safe loft floor access from the loft hatch to the tank/cylinder in 18mm (graded plywood,yes structural but cheaper ) then under the tank/cylinder the 18mm ply was doubled up. Plywood all screwed down and made safe & suitable. horizontal unvented cylinders are an option to spread point loading Thats a lot of water