Load capacity of attic floor

24 Jan 2016
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United Kingdom
Hi all,

I've recently purchased a house where the cold water tank and hot water cylinder is located in the attic. The house was extended at the side to add an extra 2 metres in width. The dimension of the extension is approx 5m in depth and 2m wide. It's within the extended part of the attic not the main attic space in which the water tank/cylinder is located.

My plumber has advised that the existing 100 litre hot water cylinder needs to be replaced due to its age and has suggested that a 160 litre cylinder would be a good replacement considering the needs of our house. However, I'm concerned about the weight - approximately 180 kg when filled.

The cold water tank is elevated on a wooden platform with horizontal supports anchored in the brick walls so there should be very little weight from this on the wooden attic joists.

The joists themselves span approx. 5m at 16 inch centres with 12 inch centres for the joists at the edges. The middle section on which the existing HW cylinder sits has been boarded with sturdy plywood which spans the whole 2m width of the extension. There is a stud partition wall on the first floor underneath but this will obviously not provide much support.

Please could someone advise whether the existing set-up could support more weight? My plumber doesn't seem worried about it but he's obviously not a structural engineer.

Many thanks.
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