How to support a heat bank on ceiling joists?

[dwtowner]

Hi all,

I am planning on installing a heat bank, to replace an existing tanked hot water system. The current tank is only 60 litres, and is currently situated in a very small airing cupboard. I have a 3-bed house, and am planning on fitting solar panels, so I want to fit a heat store of 200 litres or so. This won't fit into the airing cupboard so my only option for siting the tank is in the loft, and I would like some advice on how best to do this.

I have placed a couple of diagrams of my loft layout here:

diagrams show the main supporting walls and chimney breasts, and the joists and beams in the loft space where I want to site the tank. The diagrams don't show joists in other rooms, or partition walls. Beam A has the ends embedded in the internal walls. Beam B is embedded in the internal wall at one end, and at the end wall at the other - it is not attached to the second internal wall at any point.

There are a couple of things I don't understand here, and my `Construction of Buildings' book doesn't have any info on them either:

1) What are Beams A and B for? They only seem to be supported at each end and in places there is a clear gap (albeit only 1mm or so) between the beam and the joists underneath.Can they be used to provide support?

2) Although the joists run across an internal wall, I can't be sure that they are actually sitting on that wall - the ceiling plasterboard seems to run completely across the top of the wall. Maybe the joists are sitting on top of plasterboard, which is sitting on the wall. Is that possible? Is the internal wall providing any significant support to the joists?

The joists wouldn't support a 200litre heat store as they are, so how can I add the necessary support? The tank would have to be placed more or less on the centre line of the roof, to have enough height. From researching the problem on the web, there seem to be several solutions:

1) build a platform across the entire roof (i.e., extra beams running parallel to the existing beams A and B and perpendicular to the joists) to spread the load of the tank across all the joists 2) sistering a few joists to make them strong enough to take the load. 3) install extra beams between the two internal walls (using joist hangers) dedicated to supporting the tank, thus completely avoiding interference with the joists.

Any advice on which solution is best would be very gratefully received.

many thanks,

dan.

[Roger Mills]

The 3x2 joists are weedy, and are incapable of supporting anything other than themselves and the ceiling, however much 'sistering' you undertake.

I would be inclined to install some steelwork between the two chimney walls, and build a platform on that which is entirely clear of the joists - so that's more or less your Option 3, but using steel instead of wood.

BTW, I like your drawings. What software did you use?

[robgraham]

I don't suppose that it's possible to put the tanks on the groundfloor on the basis that because the system is at main's pressure, feed via gravity isn't necessary.

Rob

[Doctor Drivel]

Good approach using TGI "i" beams. Depends on length between the walls.

300mm TGI's should do it.

Steel? He can use wooden TGI "I" beams (Masonite beams) They will hold it and are very light indeed. The suppliers or makers will advise on depth. You only need 4 of them. on each joits to support a heat bank

One wall can hold up one end of the beams. Have vertical beams secured from ceiling joists to rafters - have these if possible secured over wall beneath. Tie in the support beams from these to the wall. Put a vertical beam on each joist (about 4 or 5) to spead the load and put the heat bank near the wall on 22mm ply screwed to the supporting beams. This will spead the load too and make the whole structure stiff. Depending on the supporting TGI beams length it may be worth having a support upright from the ceiling joists to these, to again spread the load.

[John Rumm]

They look like tie or strap beams. They would usually be nailed to each of the joists, at "thirds" of the way along. The purpose is to tie the joists together and provide some extra lateral restraint, and prevent them twisting. They also aid a little in load sharing between the joists (although not that much since their fixing is just nails acting in tension).

It could be either. Older properties would tend to have a central supporting wall. Other clues would be things like struts from purlins being taken down to loft floor level at this point. You have not included any dimensions, but assuming the drawing is to scale, then the span looks a bit on the large side unless that wall is load bearing.

What is under the wall on the ground floor?

Don't fancy that.

This would work - but I would suggest completely decoupling the new joists from the old and also the ceiling below e.g. one option would be taller joists parallel to the exiting beams but placed in the gaps, and with a 1" pad under each of the bearing points such that there is a gap between the underside of the joist and the ceiling below.

You may find this page shows it better:

3) install extra beams between the two internal walls (using joist

Yup, on a flat wall mounting shoe on each of those internal gable style walls would also work. You would loose a little headroom perhaps, but then again could probably get away with shallower joists.

Of the two, I would probably go for the second since you don't have to worry about disturbing the tie beams that way, but it may come down to which is most cost effective and gives you most free height.

Of the available joist types, steel will give you the lowest height, but will need fabrication and cost a bit more. Straight wood is cheapest and easiest to work with, but may not achieve the strength you need with sensible sizes. Flitch may be a reasonable compromise. The composite beams don't really have any special advantages in this situation (their main claims to fame being they are light and easy to move about, and very uniform in size and straightness - they are not hugely strong or shallow.

For the purposes of this exercise it might be worth downloading the demo version of superbeam from:

will let you play with wood, steel, and flitch beams and see how it all works out with your expected loadings.

[John Rumm]

Google sketchup by the looks of it...

(type "sketchup" into youtube for some nice demos and tutorials on what it can do)

[dwtowner]

Superb software: extremely easy to use, produces properly dimensioned and scaled drawings, loads of extra plugins for drawing complex structures, a huge library of pre-built components, and its FREE! You just need to invest a bit of time viewing the videos on the home page, and playing around. I've used it to produce plans for Planning Applications and Building Control.

Thanks for your help everyone. I will ponder the answers this evening...

regards,

dan.

[dwtowner]

I could do, but that would take up a lot of space that is being used for other things. I'd rather put it in the loft, which is just dead- space.

thanks,

dan.