Brief burning smell occasionally coming from under floor

[GudrunBrangwen]

We live in a converted 3 storey house; we have the top floors and there is a neighbour downstairs who has the ground floor.

We've been here about 9 months and before that we were renovating so about a year in all.

During the winter and spring we noticed sometimes a burning smell in our hallway (first floor, so landing really) between the landing and the front room.

I have taken up the floorboards, as we still have no carpet in this area, and checked the wiring which all looks fine - no sign of anything burning at all. We had a full rewire last year and so ours is all new; I cannot vouch for our downstairs neighbour though (but electrician did not comment that it looked dodgy, just probably around 10-20 years old I think).

So it isn't that. It's only in that place and only for a few seconds, and then it goes.

I've asked the woman downstairs, who is quite elderly but still sensible! and she says she smells it too sometimes, in the same place but downstairs.

I said it happened last week for the first time in a while and she said she'd put on her boiler then - which tallies with it as the weather was colder when we noticed it before, too. She thinks it is that - however the boiler is at the back of the house, maybe 15 metres from the place where we smell it.

I don't think therefore that it can be linked to the boiler wiring, and why would a boiler smell like wood burning, anyway?

Smells can travel of course and I've asked her to keep her nose on the alert so we can try and pin it down - but I am quite worried about it.

Any thoughts very welcome. I guess if it's been happening for months it's unlikely to start a fire any time soon but do not like taking risks in this regard, so knowing where it's coming from would be a weight off my mind.

Not exactly the same symptoms but...we thought there was a smell of smoke in this house when we moved in and occasionally it would seem stronger than at other times. When we moved the free standing oven to clean, we found it had slowly been leaking heat through the bottom and had burned a hole through the Lino, hardboard and through to the floorboards; in some places we could see the foundations below!

We had lighting with a transformer (90s bulbs on wires in a kitchen) and had put in the wrong wattage bulbs; the transformer was merrily burning and one day exploded. Any transformers?

Oh goodness at the oven!!

We have just had an oven fail which caused the terminal block at the back to melt - strong smell for a couple of days and I isolated it and am getting a new cooker now I know what it was.

We also have no transformers operating here, though I can't speak for 'her downstairs'

She seemed a bit defensive when I was asking about it this morning so I didn't like to push it. She is sure it's her boiler.

Now I think about it, the smell was along the hall last winter - nearer the back of the house (we have a long landing front to back) and it could theoretically be coming up through any of that area. So it could be from her kitchen, or the boiler right at the back.

I don't think I'll rest completely until we have had all the boards up in the hallway and also till she has a proper rewire which I don't see her doing, ever - though we're hoping when/if she decides to move, ever, my folks will buy her flat and then they will want to rewire it fully.

Well I'll update if there is any news!

Also the oven burnout smelled entirely different so I am pretty sure it isn't actual wiring melting iyswim. That was a chemical smell and this is more like wood. We do have wooden floors and joists and loads of dust and crap down there for kindling, which is why it freaks me out a bit. I wish I could hoover the entire ceiling space.

Do you have "trace and access" on your home insurance? That should pay for someone to investigate.... Worth asking your insurance company?

I've never heard of it. Thank you - I will enquire.

We had a burning smell regularly in the hallway of our previous home, and ex-council semi. We called in an Electrician and he found the problem very quickly. Our house and our neighbours had at one time, been joined and used by the same (very large) family. The mains electricity came in at our house and was branched to theirs when the properties were split. Our neighbours were using lots of electric heaters which were overloading our power unit and burning the wires!

it can also be a light bulb, close to the ceiling or other timber. The old fashioned incandescent (filament) bulbs get very hot, it is less likely with energy saving lamps or LEDs.

A lamp that is too powerful for the luminaire will overheat. Downlighters are especially pernicious and would be smelt upstairs. It is odd that the smell also occurs downstairs though as the hot air will tend to carry it up.

I am assuming you do not live in a wooden or timber framed house, so the wood smell probably comes from a ceiling or floor. You had better crawl around sniffing.

Electrical accessories such as switches and sockets are made of a hard plastic that will char but not melt or flame, it smells fishy when overheated, and goes brown. It does not have a plasticcy smell.

Thanks very much, yes the house is Victorian and brick built.

The thing is that the smell is so transient - it is literally there for maybe 20 seconds and then it vanishes. And seemingly only in cold weather. I think a lightbulb would smell for longer.

I have taken up some of the floor and checked, and intend to work my way along the whole hallway.

I thought it was strange that it smells downstairs, too - but reassuring in a sense as it might mean it is coming from her flat and not downwards from ours...

I'll let you know if I find anything. I had imagined it might be an electrical connection that was overheated only briefly, like when it was turned on, and then not? But would that even make sense? Also I'm not sure it would smell of burning wood if it were just wires.

Maybe she has a lot of dust on top of the boiler and that burns a little when she switches it on.?

Btw good point about the wiring being connected somewhere. I will check where it comes in and where it divides.

Maybe your mice smoke?

You imply that it smells like wood smoke i.e. not plastic burning.

You also said you've had the house re-wired. Is there a wire shorting and burning the wood?

An obvious one - are there any fires outside?

Can anyone else smell it? DO you have a kid with a good sense of smell?

Well, all circuits appear to be in good operating order and I imagine a short would have tripped the RCD so it's fairly unlikely, really, to be that - as has been said, melting wires smell different anyway - and yes, both children smelled it last week and told me about it.

When it happens it is quite strong. But it doesn't last long.

No fires outside, no.

is the boiler in a scullery or something where the light doesn't usually get turned on?

AFAIK it's in her bathroom, not in a cupboard but it could be. It probably hasn't got its own light bulb though.

I've now had the floor up most of the way along - found one cable squashed between floorboard and joist but only the outer insulation was torn, the inner wires were fine so I have taped it and put it in the notch where it belongs - need to enlarge the notches slightly just there as they have about 7 cables going through and it is a squeeze. I will take a chisel to it shortly.

The rest seems fine. I have still got just the busy bit right under the consumer unit (which for us is on the wall); I imagine that it where our supply divides, so will check it properly once I have moved the cupboard that stands there and everything inside it

I did wonder if maybe she lights her cooker with paper, as that could explain it but then I'm sure we would notice it as much in the summer?

Hmm.

Does she have a woodburner or open fire? Could be lighting it with something unsuitable?

Maybe not if windows are open?

found one cable squashed between floorboard and joist but only the outer insulation was torn, the inner wires were fine so I have taped it and put it in the notch where it belongs - need to enlarge the notches slightly

grrrr

cables should never be put in notches. As well as being squashed, they are liable to get nails and screws through them.

Tape is not suitable.

Correct action would be to drill suitable holes through the midpoint of the joist

Yes this may require cutting and joining the wires with a ratchet crimper, it is not a DIY job.

p.s.

damaged cable... wooden floorboards... smell of burning wood....

Ya...you'd think! but there is absolutely no sign of burning anywhere near it, and the wires inside the outer sheath are intact and undamaged - it had just caught the edge of the sheath and that had torn but nothing else appears damaged and I had a proper look.

I've taped the torn bit of sheath for the time being - do you think I need to get that fixed properly? I didn't think it necessary to cut and re-join all the wires as the internal insulation was fine. I have put a lot of insulation tape round the breach in the external bit so it will be strongly protected and undisturbed once the notch is a bit bigger.

Rerouting all the cables through holes would require an enormous number of cuts and crimps and I don't think I would feel any safer with those tbh.

I am very careful about the nails and screws and have checked and re-set many of the floorboards throughout the house as a lot of them had to be taken up, so are now fixed with screws and not nails, and cables/pipes are marked on the boards (at least some of them).

No one's going to put anything into the floor with screws/nails while I live here at any rate - though yes, it's been done by some bodger in the past, and the work we had done was done properly with centre-joist holes drilled. Well, much of it - they used existing notches for some of it as to drill through in the same area would have weakened the joist too much apparently. So this must be her wiring I think.

Have checked the remaining bit of under-floor and it is all fine.
So it must be coming from either downstairs, or inside the walls possibly, though I blooming hope not!

No woodburner btw but she might have a gas fire I suppose. I'll continue the detective work!

you probably only need to cut the cable once, and poke it (or a new piece) through all the holes, then rejoin.

Tape unravels after time. It will not provide the same degree of insulation and protection as the original cable sheath. Shrink-wrap sleeving, or crimps with integral heat shrink, are suitable.

Thanks, PJ. I think I'll ask an electrician to take a look (if I can get hold of one). This isn't the only cable, there are about seven going across the same joist and further, all together. I really don't want to have to cut and thread through with all of them (or rather, for someone else to have to do that).

The notches are already quite substantial but not particularly integrity-threatening, and the bottoms of them are uneven so a couple of lumps chipped out with a chisel ought to make all the difference, and the cables will no longer be in contact with the floorboards above them.

See what you mean about the tape degrading over time. I will get someone to sort that bit out properly.

Appreciate your help

Would self amalgamating tape do it do you think?

I mean as I can't get to the end of the cable without cutting it anyway so can't apply a sleeve of the heat shrink sleeve.