Woodworm in the floor joists...

[overlander matt]

During removal of carpet grippers and underlay in the main lounge, I have come across my first unpleasant find of the new project... The floor boards either side of the chimney breast recesses were a bit loose and underneath I found rotten joist ends. All 3 on each side have had it but the damage does not seem to extend back too far and, on the whole, there is hardly any damage to the floor boards.

Having read a few threads posted here previously, it sounds like I need to cut off the damaged section and use a sister joist. A slight complication I can see is that the timbers in my house are not a regular shape so won't bolt squarely and conveniently to the original. I've not removed many boards so far so that is my next step. There seem to be lots of sleeper walls below the boards and I don't see any sign of any form of ventilation - the house was built in the late 18th century.

Is there a suitable DIY treatment that can be applied to any suspect timbers? Presumably there us no need to trouble the conservation officer when lifting floor boards to carry out repairs?


Thanks in advance for any recomendations.


Matt

 

[george2019]

Woodworm only tends to affect the outer few mm, so a standard treatment painted on is sufficient if it is a live infestation. However, it could well have already been treated and there's no point doing it twice. The only way I know is to monitor to look for signs, unless someone else has a better suggestion...?

The rot is potentially the bigger problem. Large or odd shaped timber may be better suited to scarfing than sistering. But that is more difficult to complete.The cause of the rot is always too high a moisture content. This could be due to a lack of ventilation (e.g. blocked air vents), ground levels too high or water penetration through the walls to joist ends. This needs to be remedied as well.

 

[malcolm]

Wouldn't bother extending the beam or sistering - you've got ground a few inches below so much easier to build some additional support under the good bit if you are concerned.

I've not used any chemical treatments on my rot. As above the only way to prevent fungus and insects is to make sure the area well ventilated.

 

[overlander matt]

A bit more investigation today in the other front room revealed further problems... I pulled up a couple of boards ahead of a visit from a gas engineer to cap off the old gas fire pipework. The good news is the joists here are certainly more regular, making me think the irregular ones were probably only extended through to the alcoves to the sides of the chimney breast so perhaps the sistering can be considered... The bad news is that there has been further woodworm attack on the joists as I have tried to show in the couple of photos.

The first room has had very few boards disturbed over the years and they're about a foot wide! That would suggest there would probably not have been any treatment of the timbers. Is that a fair assumption? The floor in the second room has been butchered considerably - here the old boards were only six inches wide but there have been a few sections replaced in the 1980s and a rather hefty set of pipework for a central heating system fitted. Again, I suspect limited treatment has been tried previously.

As a grade 2 listed property, am I ok to start lifting floor boards with a view to repairing the floor joists and hopefully preventing the rot from getting any worse? I suspect many will need to come up. So far I have only pulled up those which have been removed to run cables and pipework. Inevitably, a few boards will not survive the experience - particularly those already damaged.

It's hard to know what I will find. This is a Georgian house and appears to have lots of supporting walls beneath the joists - my old Victorian place only had one supporting wall supporting the joists. It would seem that I need to sort out the underfloor environment to prevent damp. There are no obvious sources of ventilation which is not ideal. I guess too that repair and treatment of the joists will be necessary. If there is a good DIY product then that would be ideal.

Thanks for the suggestions.

Matt

 

[george2019]

Remember that woodworm should only be able to survive in damp wood, so resolving damp is the key issue here.

 

[88v8]

Cuprinol 5 star is a good treatment.

Air vents
https://www.castironairbricks.co.uk/
need to be inserted. The more the merrier. Hopefully the external ground levels are not a problem.
Paint them before inserting. Eastwood Extreme Chassis Black is good.
https://www.frost.co.uk/eastwood-extreme-chassis-black-primer.html
and
https://www.frost.co.uk/eastwood-chassis-black-946ml.html

Unless you are going to be standing heavy furniture on the floor in that area, I wouldn't worry too much about edge support, but if you do want to take the joists back to the wall, some dpc around the ends will save a future owner from having to redo the job in 50 years time.

Floor boards, no, if you plan to replace them like for like - salvage yards or new - no need to bother the CO.

Sometimes it is better to punch nails through the boards with a punch and a big hammer, rather than trying to lever them up.
https://www.ebay.co.uk/itm/Draper-Tools-Expert-Five-Piece-Octagonal-Parallel-Pin-Punch-Set-3-6-mm-13041/372662723433?hash=item56c46de369:g:YtkAAOSwhBtcyd-x

It depends. Sometimes the joists have dried out since the house was built and the nails are loose and come up easily, sometimes if there is or has been damp, the nails are rusted in and you will never shift them.

Where you have original boards, preserving them should be the priority, and the usual methods of getting them up - bolster chisel and hammer - are not good enough.

The usual problem is starting them. That first joist. It is often better to cut the board adjacent to the joist, and then nail or screw - brass, slot head - the board to a noggin when replacing it. This saves having to lever up the first nails from the sides.
This is self-starting without a pilot hole, grab it now.
https://www.ebay.co.uk/itm/Vintage-Delway-Berkshire-Model-TC5-6-Floorboard-Cutter-Good-Condition-13109/123700686389?epid=858007272&hash=item1ccd22ae35:g:0xYAAOSwKMRcxe6U
I bought one new, 43 years ago. One applies pressure with the foot on the platform.

Once you have the board free at one end, it is usually possible to lift it without more damage.

If a plumber or heating engineer is doing the job, they are unlikely to be interested in your boards. Bash and crash may be the theme. Sometimes one really has to do things oneself.

A thought; If you have sufficient space under the ground floor, you could do what I did in our first house; I plumbed the heating from beneath the floor. Blowlamp, water pistol to put out the inevitable fires, someone to pass the pipes and fittings and solder etc. Drill the holes from above of course, then make the joints from below. It is easier in that case if all the pipes in the room run to one access point, perhaps eccentric in terms of the piping but better than taking up a lot of boards or having to crawl around the edges of the room.
A thought.

Bear in mind of course that pipes should be drilled through joists, not notched into them.


Ivor

 

[overlander matt]

Thank you Ivor for your very detailed reply. Short of coming over and lending a hand I cannot think of anything more helpful! The time you have taken in sharing your knowledge and experience is very generous. Thank you.

It's interesting that there are no air vents around the house. I guess I will need to discuss any additions with the conservation officer. I'm also amazed at the number of supporting walls and the absence of any gaps built in to encourage the movement of air. Looking ahead to a time when the work to the joists is complete and the boards relaid, would it be better to carpet the room or have the boards exposed?

While the boards are up it will be convenient to rewire and start afresh with the central heating system so I do see some good coming from this work.

Thank you once again.

Matt

 

[88v8]

...would it be better to carpet the room or have the boards exposed?

You're welcome.*

Once you have good underfloor ventilation, then firstly there's no benefit from the boards being bare, and secondly you probably wouldn't want the draught anyway!
Although of course a stained perimeter might be a valid 'period' decorative treatment if you so wished.

Ivor

*there is a term for 'detailed' answers, I believe it's LWOG (Long Winded Old Git )

 

[overlander matt]

A quick update on some work to expose the floor joists... The boards came up pretty easily thanks Ivor with just a few needing intervention from the nail punch. The joist look like they have come out of another building at some stage.

There are 10 joists in the first room and only joist nos 3 and 4 (from the left) are supported by the external wall of the house. The first two were a good 40cm short and the rest of the original joists have been propped up with wall bricks and are generally not in great shape but I think cutting off the last 40-50cm in each case would take them back to something solid. Just thinking about the way forward here...

Build a supporting wall - I notice the original supporting walls were just laid on the bare earth. I had planned a more solid footing with some blocks and using some older wall bricks to build supports under each joist. I was planning on leaving some gaps in the brickwork for better air circulation. The other original walls don't look terribly well constructed but have lasted 200 years plus.

Fit airvents - I suspect this will need LBC which we are already in the process of applying for to make other changes to the house. In a 5mx3m room, how many would you suggest?

Joist repairs - typically the joists are 100mm square and 2.3m long. There might be some merit in replacing a couple in their entirety but the others could be cut and jointed under the new wall. Would it be reasonable to use new timber?

Thanks in advance for the helpful advice.

Matt

 

[george2019]

Building control requirements (I use NHBC as they are the same as Building Regs but are easier to follow):

"Voids should be ventilated by openings providing not less than 1500mm2 per metre run of external wall or 500mm2 per m2 of floor area, whichever gives the greater opening area.

Ventilators should be spaced at not more than 2m centres and within 450mm of each end of any wall. Air bricks should be ducted through cavities and be unobstructed.

Every part of the void under a timber suspended ground floor should be thoroughly ventilated through openings on at least two opposite sides. Where this is not possible, effective cross ventilation from opposite sides should be provided by a combination of openings and air ducts.

Provision should be made for ventilation through partitions and sleeper walls. If necessary, pipe ducts should be incorporated in adjoining solid floors, separating walls or other obstructions. Ventilation should not be obtained through a garage."

http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2011/Part5/section2/default.htm

It depends on the external walls arrangement, but for example, in a 5x3m room, 7500mm^2 of ventilation is to be provided, ideally on two opposite walls. If one external wall is 5m, then the calculation is also 7500mm^2. A standard air brick is 6000mm^2, so two would cover it - but needs logical thought, one per 'bay' of the sleeper walls would be sensible and position to create a through flow of air. Also check if you go for more traditional air bricks, the cross sectional area may be less.

Hope that helps.

New timber - I cede to others more experienced with older buildings but I think new is better in this case (I focus more on the structure than the conservation!). Not much historic merit in ground floor joists??

New supports - remove organic material, get to the same formation level of the other supports and build up from there. Not much else you can do in this situation.

 

[overlander matt]

Thanks George2019. Unfortunately the room only has two external walls and form a corner. I will ask the conservation officer about addition of air bricks - I can see this will need consent as we are putting together a larger application at the moment. I'm not sure why none were fitted originally.

As for the supporting wall, I had planned to build it with old bricks and some dense blocks that were already under the floor. My first inclination would be to build it with cement rather than lime as it is tucked out of the way and is not critical to the breathability of the house. As a newcomer to the period property game, is this a faux pas?

Thanks as always.

Matt

 

[Flyfisher]

Requiring consent for air bricks seems a bit extreme, though if you’re making an application for other items then I suppose it’s easily added.

As for using cement, It could be considered a faux pas in the sense of it being a structural material not available at the time the house was built, but there are many other examples of modern materials being ‘officially’ endorsed when repairing period properties - breathable roofing membranes being just one example.

But it raises another interesting question; in the context of period properties, are there any circumstances where the use of cement is actually better than the traditional use of lime? I can’t think of any.

 

[george2019]

Requiring consent for air bricks seems a bit extreme, though if you’re making an application for other items then I suppose it’s easily added.

As for using cement, It could be considered a faux pas in the sense of it being a structural material not available at the time the house was built, but there are many other examples of modern materials being ‘officially’ endorsed when repairing period properties - breathable roofing membranes being just one example.

But it raises another interesting question; in the context of period properties, are there any circumstances where the use of cement is actually better than the traditional use of lime? I can’t think of any.

Benefit of concrete/OPC cement is it's a lot quicker to cure. It's been around since mid-1850s but not typically used for houses until much later. In the ground as a foundation I have no issue with it being used on period properties and it's the superior choice from a structural point of view (partly due to better quality control and regulations as compared to lime/stone products) - although there are alternatives for environmental reasons. Once you bring in softer bricks etc, then lime is the better choice.

 

[Abi Cott]

Requiring consent for air bricks seems a bit extreme, though if you’re making an application for other items then I suppose it’s easily added.

I'm confident my CO would expect me to apply for consent for airbricks. I certainly require it for an extractor fan vent and I've been told there is no guarantee I would get it.

 

[Flyfisher]

Benefit of concrete/OPC cement is it's a lot quicker to cure. It's been around since mid-1850s but not typically used for houses until much later. In the ground as a foundation I have no issue with it being used on period properties and it's the superior choice from a structural point of view (partly due to better quality control and regulations as compared to lime/stone products) - although there are alternatives for environmental reasons. Once you bring in softer bricks etc, then lime is the better choice.

I understand that cement is a lot quicker to cure than lime, but that's really only a temporary benefit, typically a convenience for the builder. I was thinking more about the long term benefits, or otherwise, for the building itself. Better QC is a good point, as is foundation work. But as you point out, there are alternatives that are environmentally better so is it correct to conclude that the only real reason for using cement is for the convenience of builders?

I'm thinking here about mainly domestic buildings rather than massive structures such as bridges etc where, presumably, lime-based products would be structurally inferior to cement based mixtures. Or maybe not?

 

[george2019]

Benefit of concrete/OPC cement is it's a lot quicker to cure. It's been around since mid-1850s but not typically used for houses until much later. In the ground as a foundation I have no issue with it being used on period properties and it's the superior choice from a structural point of view (partly due to better quality control and regulations as compared to lime/stone products) - although there are alternatives for environmental reasons. Once you bring in softer bricks etc, then lime is the better choice.

I understand that cement is a lot quicker to cure than lime, but that's really only a temporary benefit, typically a convenience for the builder. I was thinking more about the long term benefits, or otherwise, for the building itself. Better QC is a good point, as is foundation work. But as you point out, there are alternatives that are environmentally better so is it correct to conclude that the only real reason for using cement is for the convenience of builders?

I'm thinking here about mainly domestic buildings rather than massive structures such as bridges etc where, presumably, lime-based products would be structurally inferior to cement based mixtures. Or maybe not?

The convenience of builders means cheaper, which means more money can be spent on more important/historic things! Now that labour is the biggest cost, time saving shouldn't be underestimated.

The more environmentally friendly foundation solutions do have some drawbacks, whereas some type of concrete solution will always work. I've never managed to convince anyone to use stone footings, but I'll keep trying. I also wouldn't use them on modern houses as there'd be too much movement for the walls to cope with.

As for limecrete, to my knowledge it's not structurally competent enough to replace reinforced concrete. One of the massive benefits of concrete is how well understood and consistent it is, which cannot be said of limecrete. Don't despair of concrete entirely, though, cement replacement materials (pfa, ggbs etc) have been around for a while and research continues to reduce the ecological footprint.

 

[overlander matt]

Interestingly, I had a visit from a structural engineer on Friday to look at a number of problem areas in the building. On seeing the floor joists he thought they were a bit far gone and asked 'why bother trying to repair them?'. So I wonder is he right or are the joists worth trying to save as I have so far assumed?

I would rather not have to get LBC in this case as I am keen to make some progress with CH pipework and rewiring which I think can only be done with the floor joists in place. This pushes me in the direction of repair. The next issue is the nature of the repair. It seems that a supporting wall is necessary if I am cutting the ends off the rotten joists. The structural engineer recommended using common treated structural timbers for the repairs but I wonder whether there is a conservation solution here with a more similar size eg 4x4 or 3x5 (which might not be so readily available).

It sounds like I need to make up some lime mortar for my wall. Given the under the floor nature of it, can I simply use a sharp sand and lime mix in a particular ratio?

Thanks in advance.

Matt

 

[Matt Green]

Every part of the void under a timber suspended ground floor should be thoroughly ventilated through openings on at least two opposite sides. Where this is not possible, effective cross ventilation from opposite sides should be provided by a combination of openings and air ducts.

That's a modern specification though. It is neither necessary nor required for a suspended floor to function.

 

[george2019]

Yeah - we engineers tend to say replace! Your reasons for repairing is good, although it will be more difficult to work with.

Below DPC/ground a NHL5 would be wise. That's a 1:3 ratio from memory, although talk to your lime supplier to be sure.

Every part of the void under a timber suspended ground floor should be thoroughly ventilated through openings on at least two opposite sides. Where this is not possible, effective cross ventilation from opposite sides should be provided by a combination of openings and air ducts.

That's a modern specification though. It is neither necessary nor required for a suspended floor to function.

It's to keep the moisture content of the timber low enough to prevent rot, the reasoning applies equally to historic and modern construction.

 

[Matt Green]

That's a modern specification though. It is neither necessary nor required for a suspended floor to function.

It's to keep the moisture content of the timber low enough to prevent rot, the reasoning applies equally to historic and modern construction.

Even if there was no ventilation and the air was at 100%RH, the resulting moisture content in pine will be about 23% at 22C which is too low for fungal spore germination. Ventilation might help keep the moisture content low enough to dissuade insect attack, but in pre-treated modern timber there is no risk of attack as long as it doesn't get wet.

My point is there isn't any reasoning: it's proscribed thinking from the 1950s/60s/70s when pre-treatment was rare and poor quality timber with a high sapwood contents was more routinely used. Smacking holes in old buildings to meet modern ventilation requirements dating from a period of history where risk was higher is pointless. There are plenty of Victorian floors without modern ventilation have not suffered at all.

I'm not saying its' a bad thing to do if you have the option, but is not a requirement and it should not be viewed as necessary in all situations (essentially: it's not what you are presenting, it's how you are presenting it).