Reinforcing a beam below an original fireplace

[monmaison2009]

Hi - Our fireplace and surrounding area has been sagging for the last 7 years or so. Two months ago we got a structural engineer to have a look and he confirmed we should be reinforcing the wooden beam below the fireplace. He recommended sistering the troubled beam and raise that area of the floor that is sagging to be at the same level as the rest of the floor in that room. We have not done any work like this before and obviously we would like to get someone who is careful and sympathetic to an original fireplace, original wooden floor and wooden beams. I would really appreciate if you could recommend someone who you have used before for work like this please. We are in N1. Many thanks

 

[MikeG]

Just checking.....this is a masonry fireplace resting on a suspended timber ground floor, which is starting to sag under the load. Is that right? That sounds a little odd.

 

[monmaison2009]

Hi - no it has not "started to sag", it has been sagging for many many years (although I was not at the property back then). We did some repairs to the fireplace marble, hearth and put back the cast iron insert (it was closed with bricks), which was made the sagging a lot worse we think hence why we decided to get structural engineer to come and have a look. Also when repairing the marble surround we saw the insert brick arch slightly collapsed on the side where the sagging is worse. I do not if this is also related to the weak beam. Please let me know if you have any other questions as we are keen to find the best solution we can (which might not be sistering the beam? We do not have much experience here)

 

[MikeG]

So the rest of my question was basically right? I'm an architect. I want to know what I'm dealing with before I offer an opinion.

 

[monmaison2009]

Hi - Yes to "this is a masonry fireplace resting on a suspended timber ground floor", you are correct

 

[MikeG]

Well, whatever timber you put under there it will always be on the move, and never properly supported. What sort of clearance is there to the earth below the floor?

 

[Kearn]

Hi - Yes to "this is a masonry fireplace resting on a suspended timber ground floor", you are correct

Not knowing the age of property, nor seeing photos which would help, what follows is obviously generalised assumption.
Shouldn't really be resting on a suspended timber floor. Your hearth should be solid at ground surely and any protruding structure which does need to be suspended into the room, adequately supported.

I'm not really sure what you mean by beam under a fireplace, there should be no wood under your piers and fireplace walls or supporting the internal hearth within the opening - so if there is, then this is a more substantial job than some extra wood.
Your fireplace piers should go down a decent level of courses beneath earth level and rest on substantial supporting stones as the foundation for the fireplace(s) and stack above, as with your walls, so if you have movement in the arch and pier(s) that is very different to just a hearth dropping.

If the existing wood structure under the protruding hearth front isn't doing it's job as per the suggestion - what's the cause, not the temporary fix?
1) Adding more wood implies the existing wood is shot - is it damp from close proximity/contact with the earth/other leaks and moisture? If one piece of wood has failed, so will another in time. I had floorboard rafters supported on more perpendicular rafters directly on the ground in some parts of my later added suspended floor rather than resting on brick walls! Not great at stopping moisture rising!
2) If the wood is still in good shape then it implies that it's structural support onto the earth is moving, or the earth itself, and needs to be remedied rather than the wood.

 

[Flyfisher]

Seems strange to me that a heavy fireplace/hearth should be built on top of what sounds like a suspended floor. I'd expect it to have proper foundations down to the underlying ground, with the suspended floor built around the fireplace/hearth. Still, I'm sure we've all seen various bodges so if it has been built on top of a suspended floor then it's not entirely surprising that the wooden beam supporting it has sagged over the years. Under such circumstances, adding another wooden beam is unlikely to do any harm but it doesn't sound like a great solution either because I'm guessing it will only slow down the rate of 'sag' rather than eliminate it altogether.

My instinct would be to add some support to the existing beam to absolutely prevent any possibility of further vertical movement, ie 'sag', but without understanding more about exactly what's under the floor it's not really possible to give definitive advice. Having said that, I'd be thinking about some sort of brick pillar(s) to support the existing beam and also possibly using a hydraulic car jack to raise the existing beam a little. It probably won't be possible to jack it back to its original position but even raising it a few mm would increase the support to the above fireplace/hearth before building a fully supporting brick 'sleeper/dwarf wall' (not sure of the proper term) underneath it to prevent any further sagging.

 

[MikeG]

I don't think we're going to be able to do much without a good series of photos of this fireplace, with the floor up, so that we can see what is going on underneath. It seems bizarre to me that someone would build a chimney stack on top of a timber suspended floor, and even if that was done when the house was built I would have no qualms about putting a proper foundation down and taking the load from the stack down to that. If it is merely the hearth that is on the floor and causing the issues, then no floor should be sagging under just the weight of a hearth. That can only mean a weak or damaged floor. It could be that it is just a decorative fire surround which is causing the issues, and if so, there should be easy fixes without doing any great structural work. So, photos please.

 

[Kearn]

If the side of the arch is dropping, is it the original opening for the fireplace? If it was an infil, then this would've / could've been built on top of the hearth or more importantly not on the original fireplace foundations and could be moving, but not as major an issue as it may seem.

Again, just guesses in the dark at the moment though...!

 

[monmaison2009]

Hi - Answers to questions to the best of my knowledge:

Building dates from 1850, it is a listed building and going as far as I can on the LB history there has not been any alterations, like putting a fireplace where there was none before, so original chimney stacks, hearths, surroundings, mantel, lintel, ... The only thing missing was the cast iron insert and the hearth was cracked
"The fireplace could be built on top of the hearth" - No, it is not
I don't think I explained myself clearly, so I will try and explain again, the fireplace is not built on a suspended floor. It is in the chimney which it is solid brick, standard early victorian construction nothing special here, the surrounding floor around the fireplace is suspended and it is sagging. Below we have the lower ground floor with its own fireplace in the same spot as the ground floor. Flyfisher and Kearn have explained it better than I did, thanks.

Flyfisher quote:
"I'd expect it to have proper foundations down to the underlying ground, with the suspended floor built around the fireplace/hearth"
--------
Kearn quote:
"Your hearth should be solid at ground surely and any protruding structure which does need to be suspended into the room, adequately supported"
--------

However, what Kearn describes as "and any protruding structure which does need to be suspended into the room, adequately supported", we have weak beam(s) supporting the hearth extension into the room, "hearth dropping".

"If the existing wood structure under the protruding hearth front isn't doing it's job as per the suggestion - what's the cause, not the temporary fix?"
The fireplace is on the ground floor and we have a lower ground floor below so it is not damp, moisture etc, what's the cause? Not entirely sure as we have not open the floor or ceiling underneath however there were a lot of cables, pipes and gas pipes going through that area (we repair part of the floor around there) so I would not be surprised if the cutouts to accommodate for all that have made the beams weak

Going back to the lintel arch, three or four of the bricks were out of place by 3 cm or so, the arch was squashed a bit on the same side, I do not know if this is related.

A couple of pictures
https://photos.app.goo.gl/JBnnRfpExWSh4IPA2

 

[Kearn]

Ah - now that makes more sense!! :wink:

Regarding the oversailing hearth, sounds like you've likely pointed at the cause - over eager tradesfolk taking too many sections of wood out for cables and pipes over the years, weakening the integrity of the supporting wood frame. Only real way to tell is remove some ceiling from below and it may be very clear to see.

Not sure about the arch - I would doubt it is connected in the order implied, as the hearth shouldn't be influencing the actual stack. Are the bricks immediately under the edge of the arch which dissipates the load downwards all ok? Does it look like it has been amended in the past? Is there an iron support, has it rusted and expanded mortar joints etc? If an arch is moving, normally it is due to the support of the arch failing - often see this on windows that have been widened so the arch is no longer applying load down through the walls either side, if that makes sense.

 

[Kearn]

Actually, I assume you've already seen the hacked our sections of woodwork from above (just noticed you said you had done some floor repairs). Given the cuts usually would sit on the top surface, then re-taking up a few boards will give you a better view of the issue - check if a spirit level will sit flat on the wooden support.

 

[88v8]

Yes, there do seem to be two separate problems here.

First, the mangled joist(s) below the hearth.
Presumably the hearth slab is sitting on a concrete base, within trimmers.
https://books.google.co.uk/books?id=yi6tbmr7s9MC&pg=PA571&lpg=PA571&dq=hearth+slab+with+trimmers+picture&source=bl&ots=xxKrIjbc6u&sig=NYtBjlgxdA6_k7owh-u_4hjq0YE&hl=en&sa=X&ved=0ahUKEwjw2OLm2_7WAhUMalAKHbykAVcQ6AEIggEwFg#v=onepage&q=hearth%20slab%20with%20trimmers%20picture&f=false
So there is a lump of concrete in a box of joists, with the hearth on top?

To avoid damaging the ceiling below, yes, take up some boards and sister the damaged joist(s), either with another joist - not the quick-grown rubbish from a DIY shed, but a decent length of dense timber such as you will find here
http://www.lathamtimber.co.uk/downloads/james-latham-product-price-guide-65.pdf
- or with a length of angle iron, perhaps 2 x 2 x 0.25" screwed with No 12s or greater and/or bolted with 8mm or greater and large flat washers, depending on access.
To supply any strength, the sistering will have to extend some distance either side of the weakness, perhaps three feet if it is the main cross beam.
Not particularly difficult, except that quite a few boards will need to come up, and the services will presumably get in the way.
If the ceiling below is lath & plaster, some care needed to avoid damage.

For future reference, where services are being run through joists, they should be drilled through around 1.5/2" from the top, not cut into the surface. In this way, the beam strength is largely retained. One should never let tradesmen hack at one's house, usually they think only of their own convenience, if indeed 'think' is the correct word at all at all.

Secondly, the arch. Kearn has covered this pretty thoroughly.
It's been widened?
It's been messed with?
It was too flat in the first place?
The wrought-iron support has been removed?
The abutments have been altered?

Pictures please.

Shame that this has come to light after the room was decorated. Sod's Law, eh what?

Ivor

 

[MikeG]

.........For future reference, where services are being run through joists, they should be drilled through around 1.5/2" from the top, not cut into the surface.......

Great post Ivor, and I think you've covered everything. Just one slight quibble with the above, though. Ideally service holes should be drilled on the centreline of joists, where they are neither in compression nor tension. Further, they should only be drilled in the region 25% to 40% of the span of the joist, from either end. In other words, they shouldn't be at the ends or the middle of the joist span.

 

[monmaison2009]

Yes, I agree, a very informative and to the point post . Thank you Ivor.

TBH, the ceiling below is not the original lath ceiling unfortunately so I am not opposed to doing the work from below if that it is easier and fix the ceiling once done. We want to get some reputable builders to do the work for us and to avoid further "cowboy work" to be done to our lovely period house so please if any of you could recommend a good builder (we actually have other work to get done too so they have a few jobs to do if they are interested), we will appreciate it very much, we are in London N1

Regarding the arch:
It has not been widen or messed with as far as I am concerned, the wrought-iron has not been removed but it is wonky and the abutments are the original ones. I might have some pictures of what it was like when the fireplace men doing the work. I will attach one as soon as I find it

 

[Kearn]

Regarding the arch:
It has not been widen or messed with as far as I am concerned, the wrought-iron has not been removed but it is wonky and the abutments are the original ones. I might have some pictures of what it was like when the fireplace men doing the work. I will attach one as soon as I find it

Pictures would certainly help. As would a definition of 'wonky'. Is it loose? ...dropped on one side? ...not set into the same level of brick coarse on each side? ...not a uniform piece of iron?

However, from my understanding, if you're saying that the the arch iron and bricks are unmolested and the tops of the piers are not damaged, then the next place that I would investigate would be where the load is distributed to - directly down through the piers - so I would be interested in what is happening at the bottom.