Loft/Ceiling Joist construction

[nero44]

Hello,

I would like to know if anyone can share some insight about how the ceiling/loft joist have been constructed in my 100 year old victorian terrace. It's a typical 3 story house, with an outrigger to the back. I am in particular after the loft space of the outrigger. The loft has been boarded with chip board, and as far as I can tell has 50mmx100mm joists with 40mm spacing spanning left to right. As you can see on the picture, it also houses my solar batteries which weigh about 76kg.

I've also uploaded a floorplan, which shows the area underneath the loft. So there is a bedroom/office and a bathroom underneath. I can see some of the wall studs coming up into the loft. I've also indicated on the floorplan the location of the battery stack.



Onto my actual question... I am actually looking to add another battery module, which weighs 25kg. However, I am a bit nervous about adding it to the stack, so I was thinking to break the stack into two smaller ones to spread the weight. Does anyone know how the joists would typically have been anchored on the sides? I would assume they would be sitting on the outside brick wall on the left and on the right side anchored into the party wall. Would it therefore be safe to assume that support close to the party wall (where the current battery pack sits) would already be strongest as the load would be mostly supported by the party wall?

 

[Stevers]

This might be controversial and no doubt you've considered this, but my take is that you've got mass storage battery packs in an environment which can get uncomfortably hot being charged and discharged daily for what no doubt will be an extended period. Rather than the weight, which is currently about that of an average human being (me), and would be more than doubled during installation when you lift the new one in - instinctively I think I'd really want to understand the long term fire (or explosion!) risk of that type of battery in that environment.

Why lithium-ion batteries pose building safety risk

With the increasing prevalence of lithium-ion batteries in the built environment, surveyors should be aware of the distinct risks they present and how to manage them

ww3.rics.org

 

[nero44]

I have considered this and specifically have only accepted a lithium phosphate (LiFePO4) based battery sacrificing efficiency over safety. And in anticipation of anyone asking, yes this installation is fully MCS compliant and I have all certs, and yes I am aware the guideline/recommendation regarding installation of batteries & Inverters in lofts has recently changed. So today, this setup would be more difficult (not impossible) to realise.

 

[Flyfisher]

I don't think I'd be worried about adding another 25kg to a 100kg stack sitting above a wall, unless you've noticed any cracks in the rooms underneath due to the joists flexing under the weight.

I am more nervous about such batteries in the house though, which is why I had mine installed in an outbuilding. I don't even charge my E-bike battery in the house!

 

[nero44]

I don't even charge my E-bike battery in the house!

Agreed, I would never do that and there are plenty of examples where these things burned down a house. But again, we need to clearly distinguish between battery technolgy here. No ebike (not even EVs) use lithium phosphate as they are not efficient per pound of weight. For a home storage solution the weight is not a problem...(well in my case it actually is..) but putting a heavy (but safer) battery in a bike or car makes it economically very inefficient.

If I had a better location, I would have chosen it. This for me was the best location having considered all factors. I have a live temp monitor+heat alarms interlinked with entire house... it's accessible...There are no rooms above it...

Anyway, this question was more about how the ceiling/loft joist are most likely anchored into the walls if anyone knows.

 

[Cubist]

I won't labour the fire/explosion risk points @Stevers and @Flyfisher have discussed but would echo the latters concerns regarding joist flex and perhaps amplify that concern. Your research into the layout of the joists beneath that floor and how those timbers are fixed to/into the walls is obviously vital. Depending on the age of the property such timbers are commonly mounted into pockets in the brickwork but, if the floor has been modernised at some point then bearer timbers may have been fixed to the internal walls and the joists then mounted in hangers pinned to it. In my view it's vital that you understand which of the various approaches has been used and particularly where the significant 'point' weight loads will ultimately rest. It's not clear from the diagram but the battery packs seem to be located against an old chimney breast in the party wall and it could be that the timber joist bearer is merely a wooden plate fixed to this. Meaning that the heaviest loads may end up being carried on the nails used to fix the hangers and depend heavily on the fixings holding the bearer to the wall. I think you would be wise to lift some of those chipboard floor panels to thoroughly investigate and map the joist layout and how these are supported. You should be wary of any points where joist ends are supported in the brickwork of an external was as any moisture could induce rot and result in the floor beginning to sag or dip.

Also, I have no personal knowledge of such batteries and would ask whether there is any possibility of chemical leakage and if perhaps corrosion of cable terminals may be in any way chemically active and whether these products could damage or impair the load carrying characteristics of the the chipboard. A further consideration would be the possibility of damp in the attic space which can also destroy the physical integrity of the chipboard.

 

[Stevers]

You should be wary of any points where joist ends are supported in the brickwork of an external was as any moisture could induce rot and result in the floor beginning to sag or dip.

It would never be a bad thing to add some bearers along that wall under the battery packs to spread the load and increase the number of joist and joist pocket failures that would be required to dump all that expensive kit into the bedroom below. At least there's no bed under there - although if there was it might soften the blow as long as it was empty at the time!

 

[nero44]

Thanks @Cubist (et. al) that's helpful.

Just to add some more colour and address your points:
- According to my information, the property was built ca 1900. The roof has been underfelted and renewed, but to my understanding there was no structural changes to the joist. I have had to remove the chipboard on various occasions (for instance when we had the bathroom underneath remodelled) to access cables. On those areas the joists look like the original ones (hopefully slow grown strong timber) with lath and plaster fixing from below. See picture as example. This is more on the fascia side.
- Having said that, I never had to open the chipboard close to the brickwall, so that sounds like a wise starting point
- To clarify the location of the current battery stack, it sits in the "alcove" next to the old chimney breast. I understand that typically flooring in front/around the chimney breast is not made by pockets into the chimney breast, but in the "alcove" (if any) I would assume they go into the party wall. So I would assume that is the most supported location compared to anywhere else. But that exactly was my question to you guys.
- The party wall is not externally facing, so I would be more wary about roof leaks rather than moisture coming in from the other side. Either way, I have been living on this house since Summer 2023 and that loft has been bone dry throughout (knock on wood..)
- The stack has been sitting there since December 2023 and to my naked eye I cannot see any bowing or sagging of the ceiling area

 

[nero44]

Found random internet picture.. I would hope the structure would look something like this, whereas the battery stack is sitting where the green area is. The idea would be to break the stack onto two smaller and lighter ones to spread the load even further along the wall onto the hopefully brick pocket anchored joists.