Suspended Floor - sunk sleeper wall question

mGrove

Hi,

I am in the process of insulation and levelling sagging floor downstairs. House is dormer type house.

After lifting floor boards, I see now that the biggest sag in the middle of the living room is due to sleeper walls in the middle being lower by 30mm.

What is best practice to fix this? If I start attaching sister joists, should I put shims under it so they don't side twist old joist? since sister joist is only attached to old joist.

The Continental Op

No idea of best practice but my first thought was has the sleeper wall sunk and will it continue to sink? I'd check first if it has any foundation and if not add some - awkward job.

The irish answer is to rip it all up and put in a concrete floor.

If the sleeper wall isn't going to move again then just shim it. Rather than adding additional joists I'd see if cutting any nails between the existing joists where they are side by side over the sleeper wall then shimming the existing timber will give you a straight floor. Then screw the joists back together over the sleeper wall and add a good few noggins.

You can see the dip with the floor up where the joists overlap which makes me think your existing timbers may be straight enough.

mGrove

https://www.boards.ie/discussion/comment/120344269#Comment_120344269

There is foundation. I doubt sleeper wall will move. maybe another 30mm in the next 60 years which is fine with me.

Yea existing timber is straight enough, just old and full of holes from floor nails.

New timber joist are 4.8m which means I could technically remove old joists with those add on joist and replace it with one piece. However I don't why but completely replacing joists is scarier to me than adding sister joists. This means it would also make sense to then go ahead and replace the wood that joists sit on with new timber and new dpc layer.

I am planning on adding noggins.

The Continental Op

Then go half way? You can't completely span the wall if the ends of the existing joists go into the wall although looking again I don't think they do? Anyway to make it less scary replace half the joists from one side. So start by cutting the middle sections apart and then take out one section of the joist and lay your new full lenght joist up against the half thats left. If your happy with that take the new joist back out then take all the rest of the half joists out from one side. Then you have access to the top of the sleeper wall (under the still remaining joists) and can slide in a new timber to get the level correct. Then place your new joists next to the original ones remaining apply a few noggins to keep the new ones in place then you can think about removing the old remaining joists.

Calahonda52

As suggested, I would get hold of a multitool and cut the nails holding down the joist over the sleep wall and shimmy them up, a bag of double glazing shims would make the final piece easier to get right: I got a mixed bag of 100 for about 11 euro

Just be aware that the "wall" plate is only sitting on the sleeper wall so if the mortar bed moves it will be a bit of a cluster ****

chooseusername

Shame you didn't do it before slabbing the walls, then you could run a membrane up the wall, but it is what it is.

That looks like it could be 2 ins, if it's uniform the length of the dwarf wall, then as above separate the joists and a 4 x 2 flat on top of the wall, it looks like there is one on the end wall.

mGrove

@The Continental Op @Calahonda52 ah I get what you saying now. That makes sense now. I have a multitool somewhere so hopefully those nails won't put up much of a fight. For shims I have plenty hardwood planks that I make shims from. joists look straight, but I will be lifting all floor boards and survey the whole floor over the coming days.

@chooseusername yes its just the way it worked out. various constraints plus doing the work myself. However from reading up and chatting to people, breather membrane and then airtight membrane should be going up on finishing wall. It doesn't makes sense in my head for membranes to be attached to cold wall, then battens on it, then 90mm insulated board... anyhow that's discussion for different thread.

chooseusername

https://www.boards.ie/discussion/comment/120345241#Comment_120345241

Sorry, didn't make it very clear, I assumed you were going to insulate between the joists and the membrane I mentioned is actually a vapour barrier across the joists under your floor and turned up at the edges and taped to the wall, but I can't see how that can be done now.

10-10-20

And as tempting as it may be, don't block those ventilation gaps between the sleeper-wall blocks.

mGrove

Ive checked some of the joists to see how straight they are. Due to their age, they still bowed. here is an example of one the worst offenders. Around 5-7mm gap. Would this joist be fine or should I replace it? The aim here is to have a level floor since engineered floor will be installed.

Lumen

You will notice even a couple of mm on a finished floor.

Approach really depends on how much you value your time, there's a lot of shimming to do there.

10-10-20

Is that woodworm in both the joist and the sleeper-wall timber in this photo...?

Treated?

meercat

Slightly off topic but I’d consider re wiring that socket circuit when you have the boards up and before it’s plastered. It’ll make the job easier and future proof that room.

10-10-20

BTW, I think you have your answer here:

The joists themselves might be too bowed to and the sleeper has dropped. In my amateur opinion, I think that's a rip & replace.

The Continental Op

https://www.boards.ie/discussion/comment/120348328#Comment_120348328

You have given me an idea there? I firstly thought all the joists were like the OP's first picture which would be a mess to add "sister" joists to. But seeing the majority are straight across in one I've changed my mind.

The original joists have bowed and are unlikely to move further so no need to mess with any of the existing joists or the bedding on the sleeper walls instead just screw/bolt you new sister joists alongside the old ones. Obvioulsy you are working to a level and need to get the tops of the new joists all the same. If the new joists are slight deeper than the old ones its OK to notch them slightly to fit them over the sleeper wall.

Down at the end where there are overlapping joists take one end out and fix to the remaining one.

I'd also give the existing joists a good dose of low odour preservative/woodworm killer while they are exposed but some people would have a different view on that.

mGrove

https://www.boards.ie/discussion/comment/120348316#Comment_120348316

will treat existing timber yes. new joist timber is treated. Seems like this was a past woodworm problem. All timber is dry, no sign of dampness.

mGrove

https://www.boards.ie/discussion/comment/120348370#Comment_120348370

this picture should explain the room better

old joist are 110 x 32 while new timber is 100 x 44.

So options are:

• Rip up old joists and replace with new one with shims under. Risk dislodging wall plate etc
• Add sister joists along side with shims under sister joist to stop it twisting.

For joist that have add on I am considering replacing them with full length.

10-10-20

https://www.boards.ie/discussion/comment/120348370#Comment_120348370

I'd prefer the sistering option too, except there are three assumptions at play there though... Whether the sleeper wall is not going to move over time and with increased load, that the timber on the sleeper is sufficient for the job and increased load and that the bedding mortar is intact.

Again I'm tempted to say that all three of these concerns would lead me to start planning on replacing the lot.

mGrove

https://www.boards.ie/discussion/comment/120348414#Comment_120348414

Very good points.

• wall movement I am not concerned. house was build in late 60s. I will assume the sleeper walls have settled by now.
• Timber on sleeper wall looks solid. There are few patches where there are signs of woodworm. I would bet its was a problem in the past due to poor ventilation. Old floor boards took the brunt of woodworm..all removed now.
• This is a living room that just gonna have a couch, tv and dining table so no heavy furniture.

As I mentioned, I will replaces some joists. so not all joists will be sistered. So hopefully not a massive increase in load.

If no budget limitations I would replace the whole lot, but then I would just put concrete floor.

Calahonda52

so is the sag only in the "bay"?

Sister joist will make insulating/fitting membrane much more difficult

mGrove

old joists are 110mm, and new joist I have are 100mm. I need to replace couple joist.

In order make new joist same height, I was thinking of adding a hardwood packer underneath the joist with wood adhesive. Then skew nailing it to sleeper timber.

Would this be sound enough approach?

The Continental Op

Hardwood packer is fine but if your new joist is fixed to your old one a few noggins will have a similar effect. Rather than nails I'd use screws but I always use screws. I'd clamp the old and the new together then fire in a few 6 x 100mm part thread screws with an impact driver. Probably not room to easily put them in square so they'd probably end up at an angle which is why I'd clamp the joists together (so the joists don't move as the pull together as the screw tightens).

Unless is was just one or two joists that needed replacing I think I'd do all of them so the spacing between the the load bearing areas remain the same? Again thats just me.

10-10-20

The overview photo helped a bit as I could see the bigger picture. It's a much larger room than I had imagined and it's a more modern house, and that changed my considerations significantly. I must also add that it looks like a significant DIY job, so well done for taking it on.

I think that packing/shimming is the way to go and replace any joists which are out of spec (define a spec for yourself). The one comment that I'll make is that I think that hardwood might crack when skew-nailed, but I know that builders used to prefer slow-grown soft woods such as pine or cedar with good ring density. Maybe ask in a builders-providers for such.

Last point from me is: this is also now your only chance to check the existing joists for flex (at the midpoint) and you might also consider reviewing the joist interval in case you want to strengthen the floor. I know that's asking a lot of "a simple DIY project", but none of mine have ever not suffered from scope-creep to the point of doubling. ;)

Doolittle51

I did something similar a couple of years ago, but replaced all the joists and floor plates too. My sleeper walls weren't in great condition so I had to replace some bricks etc. House is a similar age as yours. Just bear in mind that the floor plates on the sleeper walls are probably just laid on a bed of mortar and not secured at all. In my case, the mortar was really dry and crumbly, so the floor plates were essentially just sitting on top of crumbling mortar. Before installing new floor plates, I levelled the top of all the sleeper walls with concrete and/or mortar, using the old floor boards for shuttering. I also bedded in threaded rod so I could bolt down the new floor plates.

I'd recommend replacing all the joists and floor plates too. It'll take a lot longer to complete, but might actually be easier than what you propose. Laying the new joists is easy once you've got nice new level floor plates. And you can choose a thicker floor plate to make up for the difference in joist height to achieve your desired finished floor height.

10-10-20

Good info Doolittle.

OP, if you do end up replacing the sleeper wall-timbers, coat the timbers with SBR and that should reduce the suck from the mortar bed and reduce the chances of it weakening from rapid moisture-loss into the timber.

mGrove

Thanks again for all the replies lads! I really appreciate the input!

This is a classic case of scope creep. I just wanted to insulate the floor, but then also need a level floor for new flooring so here we are.

For shims under the joist I might make them out of treated joist timber if hardwood cracks. I ll test both of them out. For joists that are sistered, noggins should provide support.

I am confident enough to sister joists, replace old one etc. However I think my limit would stop at wallplates, mortar etc. As I understand it's not a simple case of putting dpc, slapping some pre mixed mortar and adding a piece of timber on top. Are there bedding in and levelling procedures? I read Doolittle51 reply and that info was lost on me.

Wall plates look 50/50, some spots are grands, some spots are worse off. Mortar is cracked and crumbly in some areas. I know in ideal world, wall plates would be redone. However I am gonna leave them alone. What are the real risks? Floor won't shift that drastically and if it will, joists are 1-2 mm from walls.

There is a spot where sleeper wall timber lifted. My plan is this. Plastic packers and fill the gaps with this. (This is different room to above pic)

10-10-20

ah japers - can of worms...

I hope that's just deflection. Did that gap open up because you took the floorboards off, or was it actually like that the whole time? Was the floor loose at this point? If you step on the joists at that spot, does it close up? The leading indicator here is going to be the condition of the mortar. Is the mortar on that section complete and still sitting on the blocks, or have the blocks dropped and is the mortar unevenly sitting on the blocks? If the answers to these questions indicate that the sleeper dropped, then you might need to get a laser level out and starting mapping this out with a view to replacing the sleeper.

As to whether you should pack-out and fill those gaps... that's TBD on the basis of above, but I would not be using a mortar repair as that's just a cosmetic filler.

Doolittle's post is to do with whether those blocks are provided with a compacted stone foundation and mortar or whether they were put sitting on the compacted earth with just mortar underneath to allow leveling. If it's just soil, it may have compacted further over time if there was organic matter within. The threaded rod which he then installed would have securely tied the wall plates to the blocks, preventing deflection. Whether that's needed or not here is hard to know, but I'm thinking not.

Laying a new sleeper isn't rocket-science - but you need to know that the base is solid and not going to give way in 10 years.

mGrove

https://www.boards.ie/discussion/comment/120354644#Comment_120354644

I have only notices the gap once floorboards were removed. before that the floor felt solid not bouncy, but you could tell it wasn't even. Sleeper wall in the middle has dropped. Sleeper walls are sitting on what seems like concrete foundation, I guess compacted stone. Not earth. But I think there is layer of mortar under them too.

I am not sure what deflection means in this case. Sleeper wall timber bowing?

Condition of mortar id say 65/35, some of it is solid while, some where there is a thin layer is crumbly. Definitely there are a number of spots where there are gaps between timber and mortar bed.

Would it be an option to remove joist, remove wallplate timber with mortar and dpc. Leave blocks alone.

Then put new Dpc, new mortar, and put new timber on top? I would have to make up for the lost height, especially the sleeper walls that are in the middle of room, in some cases 30mm lower than sleeper than sleeper walls which are beside a wall, with thicker layer of mortar. But that doesn't sound right. I assume big thick layer of mortar bed is not that stable as what I have now with packers?

Doolittle51

Here are some pictures to show what I did. In my case, the sub floor is concrete, and was sloping quite a bit. I levelled everything with concrete and mortar as shown, then put dpc on top, then fixed the floor plates.

I might not get a chance to post again here for a couple of days, so apologies in advance if you have any questions.

mGrove

https://www.boards.ie/discussion/comment/120355254#Comment_120355254

ah beautiful! doesn't look too bad. this is actually giving me confidence in tackling sleeper walls. I am gonna digest this and make a decision.

10-10-20

I am not sure what deflection means in this case. Sleeper wall timber bowing?

Yes, the timber bowing following the release of downward pressure. Deflection is fine if that's what it is as long as you settle it or account for it before the floor is reassembled. Settling it would mean forcing it back into position and alignment with the rest of the floor using weight or fixings. Accounting for it would mean packing it and then ensuring that all other wallplate timbers are leveled off it. Settling is the simple option here, that's why I recommend you step on it and then run a laser level across the room and check whether they are all at the same level.

BTW OP, in the last photo the mortar under those blocks looks solid and it does appear to be a concrete floor, so that's a bonus. Any lifting of the mortar on the left of that photo is probably just deflection.

10-10-20

https://www.boards.ie/discussion/comment/120355254#Comment_120355254

High-bar set there alright. As you mentioned, you used shuttering to create the sleeper-wall bedding. I get the impression that builders just place about three large dabs of mortar down on the wall, then set the timber into this and level it off before lifting the timber and filling in the remainder of the mortar and checking for level again.

mGrove

https://www.boards.ie/discussion/comment/120355522#Comment_120355522

Ok I get you now. if you have floor plate that's deflecting - essentially separated from mortar bed then you have issues right? since I understand floor plate not resting on mortar bed is a no no.

Here is another pic of the gap, I spot various degrees of gaps on different sleepers. maybe due to floor, and then old floorboards being removed.

Here is some one previously, inserted shims. Not sure at what stage this was done but looks like old work.

After some thinking I have decided to rip all timber out and rebuild sleeper walls using  Doolittle51 pic as refs. Since I have all the tools anyway, just need to get some general purpose mortar and threaded rods.

My main reasons are not the gaps as such as I am still not convinced they pose big risk. (maybe bouncy floor?)

But in the living room, two sleeper walls there run in the middle along the room, have sunk so I would have to essentially sister every joist. Then do the same in one half of the kitchen... hallway that separates the two is ok.

Since I am sistering every joist, I would be just installing new suspended floor along old one, doubling weight on sleeper walls. Don't like that idea. I might as well delete old timber. Some old timber has signs of previous woodworm.

Sistering joist takes some amount of work too, plus installing m12 bolts with plates is not cheap.

If adding all of the above in terms of effort + money, it makes more sense to start fresh. As it was mentioned, it might take longer, but it should be easier.

10-10-20

I'm presuming that any of the wooden shims are original installations (unless you tell us otherwise) and the plastic are yours? If so these wooden shims were originally inserted to account for the differences between each of the sleeper-walls at the point where they were laid and they should be providing a level surface over-all, to which you can take an offset from (using a laser) and validate the overall levelness of the floor.

The point which I was trying to make earlier was that if you have a floor which is laid level 30 years ago and you then strip it back by unloading it mechanically and also remove the floor-boards, that floor will try to recover from the settling, deflection and changes in humidity which it was under for that 30 year duration with the result that some parts will lift slightly. That small amount of lifting is natural and will (or should) recover as you refloor the room, but you have to decide whether the gaps now observed were the results of either: recovery from loading/deflection/humidity OR settling/failure of the sleeper-wall.

I'm suggesting for that reason that you take time to map out the room with a laser level to define these differences as you may find that the floor is 95% level, but just with work needed in that one corner. I hope that this is clearer.

mGrove

from this picture you can see how far middle sleepers have sunk. so even if close the gaps I am still not level.

10-10-20

https://www.boards.ie/discussion/comment/120357741#Comment_120357741

Ok, clear. I just didn't want the point to be left hanging. Good luck with the work and I think we all do look forward to updates!

Doolittle51

You'll find 20kg bags of ready mix cement in most builders providers. I mix up about a third or half a bucket at a time, just using an old garden trowel. Same for mixing mortar. Have a look for tarmac brand ready mixed mortar. It's the only one i found thats actually pre-mixed. Most other ready mix bags have the cement in a seperate bag and you need to mix it with the sand yourself.

mGrove

https://www.boards.ie/discussion/comment/120358874#Comment_120358874

Yea I am planning on using this, K mix general purpose mortar for creating bed / level layer. and maybe slap some of it at the bottom of blocks to secure them in case some are loose. I don't really need cement, since I am not putting new blocks right?

https://www.goodwins.ie/products/k-mix-instant-mortar-render-25kg-just-add-water.html?name=%20k%20mix&type=simple

Doolittle51

You'll probably be ok with mortar. I had to make up a couple of inches or more in some places, so concrete was a better option for me.

10-10-20

Yes, those mortar bags are fine. You should try add a plasticiser with the mix water. It helps to make the mortar more "plastic", workable and lessens the need for water.

https://www.goodwins.ie/products/mortar-plasticiser-5lt.html?filter_set%5B%5D=1,1056,1083

A bucket trowel (or garden trowel) and a medium sized brick trowel - then you're sorted.

https://www.goodwins.ie/products/draper-soft-grip-bucket-trowel-140mm-81237.html?filter_set%5B%5D=5,1785,1790

https://www.goodwins.ie/products/brick-trowel-soft-grip-275mm-by-draper-81233.html?filter_set%5B%5D=5,1785,1790

Generally if putting mortar on existing concrete/block, wet it beforehand to reduce the suck (rapid removal of water) by the dry concrete.

Bass Reeves

OP another option is to get 150X50mm to use as sister joists. Notch them for the end and for sleeper walls to bring to the exact level you require. You can probable buy them treated. Brace or screw them onto existing joists. Its a different approch. I would not be a fan of depending on an 30mm of mortor cased onto the top of blocks to make up the difference it could crack down the line. I would much perfer to make up the difference with a thicker wallplate

mGrove

https://www.boards.ie/discussion/comment/120359411#Comment_120359411

You can read through the thread as I discussed why I don't think it would be a good option. Sister was considered but due to the amount of sistering I would have to do, it doesn't makes sense in this case. Plus other issues.

I am not going to put thick level of mortar. Difference will be made up with thicker sleeper or doubling.

The Continental Op

https://www.boards.ie/discussion/comment/120359502#Comment_120359502

You want a reasonable thickness of mortar. If its too thin it won't do that much good and probably crumble, particularly if you don't wet the top of the blocks before putting the mortar on them. What happens is dry blocks (could be bone dry in your case) suck the moisture out of the mortar before it has time to cure properly.

Bass Reeves

https://www.boards.ie/discussion/comment/120359411#Comment_120359411

The weight of the new timber would not actually add weight to the sleeper walls. It would actually reduce the load weight on any particular point on the sleeper wall. It the action on the floor above that put weight on the bearing points the greater the area of the transfer of that weight the lower the weight on the bearing point.

Only reason I was recommended using sistering is it makes it relatively easy to install for someone who may not be a carpenter. The new joists will carry the majority of the load you only need to brace or attach to existing joists to firm the structure as what should have been done originally. I only have used the old joist to position the new ones.

The woodworm may be an issue if the woodworm is still active. It virtually impossible to eliminate even with wood preservatives. You would only want to bolt where there is a gap and a 32mm spacer ( metal) would solve that issue.

Having said all that a complete new floor is the best solution.

mGrove

https://www.boards.ie/discussion/comment/120359595#Comment_120359595

that's good tip! ill make sure to mist some water on blocks. I am aiming for 20mm thickness as that what it was before and roughly will be give same height. Obviously it'll vary as blocks are not even.

https://www.boards.ie/discussion/comment/120359789#Comment_120359789

Ok that make sense. My thinking was, if I have to sister every joists, I might as well just have only new joists.

In addition, mortar was missing or crumbling in a number of places and I understand that putting shims between floor pate and dpc is not good solution as floor plate is not attached.

I may still sister few joist in the hallway.

10-10-20

Just on the mortar discussion, not to be pedantic, but a couple of general points which I have learned:

You're not supposed to work with wet blocks as the excess water causes the bond at the interface between the mortar and block to fail (dilutes it, effectively), but you do need a minimum of moisture within the block to complete curing process as well as keep that suck to a minimum. Old blocks which have been indoors for years are going to be dryer than new or outdoor blocks.

So what I do is just wet the block about 10 mins prior and let it soak in. No need to wet it again, just apply the mortar and tap the block down into place.

Joints should be 10mm in depth. When making up the mortar and especially when using thin joints (less than 10mm), watch out for stones in the mix. You may on occasion need to sieve the material if you need a thin joint. 🙄

Mr AJ McCormack has some very good info on the topic of mortar here:

https://www.pavingexpert.com/mortars

mGrove

https://www.boards.ie/discussion/comment/120361247#Comment_120361247

Excellent! Will read this.

mGrove

Thought I would update this thread with the work I ve done. Was busy doing living room and kitchen. Going through my phone I realised I didn't take many pictures at all unfortunatly.

First of all, BIG shout out to everyone who gave me advice on how to approach this. Especially to Doolittle51 for providing photos! Massive help. Thank you.

This may not be perfect but I am happy with the result. Installed subfloor is level, solid, not bouncing. I had to buy a used refurbished nail gun but otherwise only cost was material.

definitely not as daunting as it sounds, if you have time. You spend more time making sure everything is level and waiting for mortar to dry than actually doing work.

Here are few photos anyway. I had to double stack some floor plates in the middle to make up the height.

sliced floor plate timber and joist. Woodworm had a feast at some point.

10-10-20

Well done. You can tell it's a DIY job though... it's neater than a builder would ever have done it. 🤣 👍️