Rot-damaged joists in crawl space: what's holding the house up!?

[torparavgrund]

I am about to buy a wooden house built in 1929. Good price, good location, good size. Everything seemed fine until I crawled around a bit in the crawl space. Now I'm wondering what is actually holding the house up. Let's start with the background facts:

Frame: Plank frame, later additionally insulated on the outside. No plastic, thankfully.
Foundation: Crawl space foundation, small stones at the bottom, covered with durable plastic with some stones placed on it.
Foundation wall: Unclear, actually. Smooth concrete both inside and outside, but in some spots I see that there is natural stone in it. Old natural stone wall encased in concrete? Poured a foundation wall but filled it with natural stone?
Sill: Hidden! Could not be seen without breaking something. Which I did not do since I do not own the place...
Floor structure: Wooden beams, B x H approximately 120 x 120 resting on stacked natural stone (2-3 really large stones in each place, bricks where the chimney once stood) with a block between the stone and beam, 5-6 running the entire length of the house (about 10-11 meters). House width about 8 meters. Moisture content between 14-18%. Almost no visible sagging, and nothing has warped.
Insulation: sawdust above the blind floor of boards. Bits of newspaper sticking out here and there.

Damage:
Many areas in the floor structure and blind floor are seriously rotten! In some places, it looks like it has been raining in or something. The same beam can have great variation; where it rests against the foundation wall (with a bit of tar paper in between...) they are so rotten in many places that I can push in an entire screwdriver = completely shot, while in other places I get the screwdriver in a few centimeters. Where they rest on the stones, it's also mixed, but generally better.
In just one spot, I saw one of the cross beams supporting the inner floor, and this was basically intact.

Contradiction:
How can it be that the floor structure under the house is so bad, but the house as a whole seems quite okay? Did a lot of moisture get in before but stopped when water-based heating was installed in the 70s so it dried out as the heat leaked down into the foundation? All floors inside the house are flat, level, and feel stable and firm when walked on, I also tried stomping hard here and there without noticing anything strange. Likewise, the walls feel robust and solid.

Questions:
Help me here, House Builders. Everything felt good in the deal until an hour ago.
Question 1: Is it possible to remedy this, or is it completely hopeless?
Question 2: If it is possible to remedy, can it be done without tearing up the inner floors? I already suspect "no," since available depth varies from 30-80 centimeters (it's on a slope).
Question 3: Who should I contact for a more professional assessment? Carpenter?

 

[torparavgrund]

Update: A phone call to what sounds like a credible carpenter later, I feel calmer. His response to the above is that:

• Absolutely, it can be fixed, but it will likely cost a bit, especially as they will probably need to replace the syllen as well.
• It can be done without tearing up the interior floors, but it is not recommended. The drastically increased time it takes and how inconvenient it becomes is not proportional to the benefit of saving a yellowed spruce floor from the 1970s.
• The reason all the walls feel okay is because they rest mostly on the syllen, and since it's a plank frame they hold each other up quite well even across.
• The reason the indoor floors feel okay is probably because the weight is distributed over such a large area and it's not yet so rotten on the top side and important points of the floor joists that it hasn't sunk anywhere yet.

The Plan: before moving in, I will tear up the interior floor and replace the syllen + joists. Bitter expense, but hopefully only need to do it once in a lifetime.

I will continue to comment and update here, as I couldn't find any really similar question on the forum and I want to contribute to the next person faced with something similar. Now, nothing more is likely to happen until the transfer in October.

 

[justusandersson]

Don't you think the foundations consist of masonry stones that have then been plastered? Unreinforced concrete filled with stone seems less likely, although it should not be ruled out.

A rotten blindbotten indicates moisture problems in the crawl space. Often, it was the result of lack of heat loss downwards, following the cessation of heating in the chimney and possibly increased floor insulation, although that doesn't match with the sawdust. The moisture period may have occurred earlier, but conditions may now have returned to normal. Moisture content of 14-18% in the wood is higher than it should be in 90-year-old wood, but nothing alarming.

1) It can always be fixed. The extent determines if it is realistic.
2) No, because some floor joists need to be replaced and the blindbotten wood needs to be accessed.
3) Difficult question. It depends on the extent of the damage. If parts of the supporting structure need to be replaced, it may require assessments that a carpenter cannot make. The same goes for questions about building physics.

 

[torparavgrund]

Don't you think the foundations consist of masonry granite that has then been rendered? Unreinforced concrete with granite stones seems less likely even if it shouldn't be ruled out.
----
3) Tough question. It depends on the extent of the damage. If you need to replace parts of the load-bearing structure, it may require assessments that a carpenter cannot make. Likewise, questions about building physics.

As I said, I'm not sure about the foundation. I agree it would be strange to embed stones in the concrete. At the same time, if it's rendered, they have managed to make it VERY smooth and fine, with no visible lines from top to bottom, and completely smooth and square corners for vents and where the beams rest.

What do you include in 3)? My thought is that no load-bearing parts are "replaced" in the sense of altering their function, just replacing a damaged part with a new equivalent (+ adding more to somewhat address cc600). Hmm, is this something one might need permission for, even if you're just replacing a damaged building part without making substantial changes?

Regarding the building physics, I'm quite familiar with old houses of this type, I know, for example, better than to try to incorporate plastic, ensuring good hygroscopic capability, etc. Not an expert, of course, but I understand the basics from "Strålande värme, krypande fukt". Damn good book, by the way.

 

[justusandersson]

Very good reading!

I think that if the beams are 5x5 inches, it is difficult to find new equivalents. (5x5 inches corresponds to 45x175 mm) Then you need to know what to look for. If you tear up the floors, you should check that the dimensions are generally sensible. A regular carpenter usually cannot assess that. I wouldn't worry about permits.

 

[torparavgrund]

Very good reading!

I think that if the beams are 5x5 inches, it's hard to find new equivalents. (5x5 inches corresponds to 45x175 mm) Then you need to know what to look for. If you tear up the floors, you should check that the dimensions are generally reasonable. A regular carpenter usually can't judge this. I wouldn't worry about permits.

When I dug through the entire forum for answers, the user @justusandersson came up, you seem to have a better grasp than most on beam structures, how great that you've shown interest! Could it be that we have a civil engineer on the thread? I've seen you respond with simple strength calculations in similar threads.

Please evaluate this reasoning I have:
The house was probably built by a team of carpenters with a construction foreman/master carpenter at the helm, with much less knowledge than a modern civil engineer has. But the demands for construction have increased significantly, while the quality of the lumber has decreased. We have the internet, moisture meters, and calculation programs. If those who built the house wanted to "calculate" anything, they at best had tried-and-tested experience and pen and paper.

At the same time, the house has stood for 90 years and shows no clear signs of any walls having sunk; everything looks straight, the roof is flat, and the bottom beam structure looks straight as mentioned. Even though the load-bearing walls rest on this poor beam structure.

With all this in mind, shouldn't I manage if I replace the beams that the walls rest on with, for example, laminated beams 90x315 or 115x180 or something similar? They must be clearly much more durable than what's already supporting the house, even if the beams were sound.

(This, of course, assumes properly cast footings in sufficient number and size + that I fill the rest of the bottom beam structure with a number of 45x220 as bearing lines for the new floor structure under the floor.)

 

[justusandersson]

I find it difficult to discuss dimensions without knowing the relevant spans. A simple form of blueprint, which you might have to create yourself, facilitates communication.

I am an older architect who received a very thorough education in structural engineering, among other things, as part of my training. I also find it enjoyable. Most older small houses are builder-built. The builders had no formal education in building technology, but they used tried-and-tested solutions and knew where the boundaries lay. Certain standards have been tightened, and above all, the demand for energy efficiency has increased dramatically, which has caused some problems.

 

[lärjungen]

How does the ventilation look for the crawl space? I had a project at work this spring where the subfloor of an old cottage had failed and the insulation had fallen down. When we crawled in to solve the problem, the first thing I noticed was that the ground was damp. The soil was so saturated with moisture that you could roll balls out of it. It soon became apparent that the floor joists (solid logs) were almost completely rotten. You could push a knife almost all the way through them. This had caused the subfloor with insulation and everything to collapse. It was just a matter of time before the entire floor would give way.

The cause of the moisture problems was that someone had renovated the foundation incorrectly a number of years ago. They had encased the natural stones (which made up the cottage foundation) with concrete and plaster and closed up all the ventilation openings. Had they left open for ventilation, this likely would not have happened.

 

[torparavgrund]

What does the ventilation for the crawl space look like? I had a job assignment this spring where the subfloor of an old cottage had given way, and the insulation had fallen down. When we crawled in to solve the problem, the first thing I noticed was that the ground was damp. The soil was so saturated with moisture that you could roll balls of it. It soon turned out that the floor joists (hefty logs) were almost completely rotten. You could push a knife almost all the way through them. This had caused the subfloor with insulation and everything to collapse. It was only a matter of time before the entire floor would give way.

The cause of the moisture problems was that someone had renovated the foundation incorrectly some years ago. They had encased the natural stones (that made up the cottage foundation) in concrete and stucco and had sealed all the ventilation openings. Had they left openings for ventilation, this likely would not have happened.

Yes, I have read most of the information on Ljungby Fukt och Sanering (lfs-web.se) and some books on older construction techniques. They paint a picture that aligns with yours, and I suspect the same is true for this house.

My case:
Here, too, I believe the case is that they have cast a natural stone foundation in concrete. In some places, you can see a bit of natural stone protruding from the concrete, which otherwise is completely smooth and slightly thinner nearest the sill than near the ground (i.e., it slopes very slightly outward). It looks like professionals did this considering the quality (not that it's an appropriate measure, though...).

The ventilation consists of at least two openings with metal vents, both approximately 25x25 cm, and the hatch to the foundation, 45x45 cm. I must admit I wasn't very attentive here, so there may be more.

I didn't lift the plastic lying on the ground ("Teno 20D age-resistant," I believe it said), for fear of tearing it or getting sawdust underneath. It's laid with a very large overlap. From what I can see, the ground below is covered with large-grade crushed stone, much larger than gravel. The stones were about 70-100 mm across. From experience with similar house foundations, my suspicion is that there is soil under the crushed stone, and everything likely needs to be dug out and filled with more gravel. Meanwhile, the current owner says it isn't very deep to the bedrock, according to the person who deep-drilled their well in the late 1980s. It's unclear, though, what "not very deep" means to a well driller.

The house is on a slope, and two downspouts end on the higher side, i.e., water runs towards the foundation. I need to address this regardless with drainage and piping.

I already have some plans for all this but can't really do anything sensible until the handover in October. I'm feeling incredibly impatient right now.

 

[useless]

It sounds like the most important measures have been taken to keep the foundation dry (Sealed plastic on capillary-breaking gravel). However, you should make sure that the roof drainage is directed away from the house.

Is the joist currently damp, or are there just old rot damages?

How can it be that the joists under the house are in such poor condition, but the house as a whole seems quite okay? Has a lot of moisture gotten in before but stopped once waterborne heating was installed in the 70s, so it dried out when the heat leaked down into the foundation?

It's rather the opposite. Old foundations worked fairly well because people constantly fired up heating in the past, so the chimney was warm under the house. When you modernize old houses, install other heat sources, and stop firing up heating, the problems appear like a letter in the mail (Yes, it is an old saying used in the past when letters sent always arrived to the recipient).

 

[torparavgrund]

@useless The timber was around 14-18% moisture content when I checked.

I expressed myself poorly. Of course, the construction was originally sound as long as heat was continuously generated in the chimney throughout the year. I also believe the problems worsened when the natural stone foundation was covered with dense concrete and only a few ventilation gaps were left.

I also believe that significant improvements have already been made by placing plastic over it, which has halted the damage process (or whatever you want to call it) or at least slowed it down considerably. I suspect that the damage to the joists mostly occurred before this. I believe that the water-based heating system was installed and the chimney was demolished (as it has been) during the 1970s, leaving the structure damp for many years before plastic was applied sometime in the last 5-10 years or so.

If I could get away with leaving the joists as they are and feel secure about it, I would certainly do so. But I dare not, because if it continues to slowly deteriorate/weaken, it won't be long before the "magic" that holds it together and has yet to let the heart walls collapse is gone.

I will probably still try to make even greater improvements to the climate in the crawl space, such as installing Platon mat internally against the foundation wall and then LFS-25 crawl space insulation both on the bottom and a bit up on the foundation wall (outside the Platon mat). This is because I suspect that condensation moisture, when warm outdoor air meets the cold stone in the foundation, has been a major contributor to the rot, especially where wood has rested directly against the foundation wall. In one place, I saw that some building paper was placed between the beam and the stone. It was as damaged as the rest...

Of course, with drainage and redirection of water from the ground as much as possible. I do such work myself, and the material costs are not particularly high in this case. Especially in relation to the fact that if I take all necessary precautions now, I will likely never have to worry again as long as I live there.

 

[Killen som behöver hjälp]

@useless The timber was around 14-18% moisture content when I looked.

I expressed myself poorly. Of course, the construction was originally sound as long as the chimney was heated year-round. I also believe the problems worsened when at some point the natural stone foundation was covered with dense concrete, leaving only a few ventilation holes.

I also believe that substantial improvements were made by laying plastic over it, which has stopped the damage process (or whatever you want to call it) or at least slowed it down significantly. I suspect that the damage to the joists mostly occurred before that. I believe the hydronic heating system was installed, and the chimney was demolished (because it was) in the 1970s, so it remained damp for many years before plastic was laid over it sometime in the last 5-10 years or so.

If I could get away with leaving the joists as they are and feel secure about it, I would of course do that. But I dare not, because if it is still slowly deteriorating/weakening, it's not long before the "magic" that holds it together and hasn't yet allowed the heart walls to sink in is gone.

I will probably still try to make even larger improvements to the climate in the crawlspace, such as a Platon mat internally against the foundation wall and then LFS-25 crawlspace insulation both on the bottom and partially up the foundation wall (outside the Platon mat). This is because I suspect that condensation moisture when warm outdoor air meets cold stone in the foundation has greatly contributed to the rot, especially where wood rests directly against the foundation wall. In only one place did I see a bit of roofing felt laid between the beam and the stone. It was as damaged as the rest...

Of course, with drainage and diverting water from the ground as much as possible. I do this myself, and material costs are not particularly high in this case. Especially in relation to the fact that if I cover all bases now, I probably never have to worry again as long as I live there.

Hi!
How did this project go?
Was it an expensive or reasonable renovation cost/time?

I'm about to acquire a house with similar issues, although it doesn't have any plastic and the joists have already started to collapse.

However, there is no hatch to the foundation and plastic mats over all floors, so I haven't been able to see the foundation myself yet.

But I am eagerly awaiting to see how bad it is; what did this job cost you? 😊

 

[torparavgrund]

Hello!
How did this project go?
Did it result in an expensive or reasonable renovation cost/time?

I'm about to take possession of a house with similar problems but where there is no plastic and the floor joists have already started to collapse.

However, there is no hatch to the foundation and vinyl flooring over all the floors, so I haven't been able to see the foundation myself yet.

But I'm waiting eagerly to see how bad it is. What was the cost for you? 😊

What was the cost? About 10-15k maybe? If we're only talking about measures in the foundation and the floor joists, then an additional approx. 20k for new flooring and maybe 5-10k for new insulation. That and an incredible amount of time since I did it myself. I can write a little summary of how it turned out later on:

1. The floor joists: not as bad as I first thought. Most of the joists were okay after all, and those that were in cast pockets in the foundation wall were easy to fix by jacking up, sawing away to healthy wood, and then placing tar paper and a wedge-shaped wooden block between (the thick end of the wedge facing the house). Some joists I completely replaced with standing 45x220 which I glued and bolted together to equivalent 90x220. I also put up additional "legs" that the floor joists rested on, also made of 45x220 and through bolts (18mm threaded rod + washers + nuts). The single scariest moment was lifting a central wall with jacks to replace the broken joist underneath. But that worked too.

2. The subfloor + floor: mostly so poor that it wasn't worth trying to fix. In several places completely rotten and collapsed, i.e. zero insulation up to the floor. Many bays filled with moldy and disgusting sawdust. So the decision was to lift off the floor, build a new subfloor, and fill it from above with cellulose insulation, then lay the floor back. The latter went down the drain. The floorboards (28x70) were nailed down hard with large nails angled through the tongue, often 2-4 nails per floor joist, so no matter how careful I was, the tongue would crack off, often even the bottom third of the board. Oh well. Just had to buy a new floor. Found a retailer that manufactured 28mm spruce flooring. Regret deeply that I chose such wide boards (190mm wide). It looked very luxurious from the start, but even though I carefully let it dry indoors for several months before laying it, it dried even more months after it was laid, so today I have gaps between 0-5mm across the floor. I think it looks dreadful, but I get a lot of compliments on what a beautiful old-fashioned floor I have, so that's something. The important lesson there is that a board grows and shrinks in width. If it’s say 5%, then 5% of 70mm is 3.5mm in width, while 5% of 190mm is 9.5mm...

Anyway, when everything was done with the foundation and the floor joists, I nailed a new subfloor, taped the seams, and put in new insulation, then put on a new floor.

3. The plastic: upon closer inspection, it wasn't as well laid as I thought, with numerous small holes where it had chafed against sharp stones (probably already during laying), and I could see that it had been placed over organic material in several places. Got rid of the junk, cleaned out all sawdust and other debris underneath, added a bit more gravel to the worst spots, laid new plastic with better overlap and butyl sealing between the overlaps, and made sure it went up a bit against the foundation wall. I also laid a thin insulation mat (sold as "crawl space insulation" but delivered directly from the factory, and I could see it was labeled "concrete cover mat," the retailer admitted it was exactly the same).

Summary: all steps in order were: tear up the old floor, empty all bays of sawdust, tear out the subfloor, repair damage in the floor joists, remove plastic and organic material from the foundation, lay new plastic and insulation, nail new subfloor, new insulation, new floor. All in all, somewhere around 40,000 SEK (year 2019 before the insane price increase during Covid) and AT LEAST 250 hours of my life. Worth it.

 

[Killen som behöver hjälp]

What did it cost? Approximately 10-15k, maybe? If we're just talking about measures in the foundation and joists, then an additional about 20k for new flooring and perhaps 5-10k for new insulation. That plus an incredible amount of time since I did it myself. I can write a little summary of how it turned out afterwards:

1. The Joists: not as bad as I first thought. Most of the beams were okay, and the ones set in cast pockets in the foundation wall were easy to fix by jacking them up, sawing off to fresh wood, and then placing paper and a wedge-shaped wooden block between (the thick end of the wedge towards the house). Some beams I completely replaced with standing 45x220 which I glued and bolted together to equivalent 90x220. I also put up more "legs" on which the joists rested, also made of 45x220 and through bolts (18mm threaded rod + washers + nuts). The scariest part was lifting a structural wall with jacks to replace the damaged beam underneath. But that went well too.

2. The Suspended Ceiling + Floor: mostly so deteriorated that it was pointless to try and fix. In several places, completely rotted and collapsed, meaning zero insulation up to the floor. Many sections filled with moldy and disgusting sawdust. So the decision was to take up the floor, build a new suspended ceiling and fill from above with cellulose insulation, then put the floor back. The latter went wrong. The floorboards (28x70) were nailed down hard with large nails angled through the tongues, often 2-4 nails per floor joist, so no matter how careful I was, the tongue split off, often also the lower third of the board. Oh well. Just had to buy a new floor. Found a dealer who made 28mm spruce flooring. Deeply regret choosing such wide boards (190mm wide). It looked very luxurious at first, but even though I let them dry carefully indoors for several months before laying it, it dried even more in the months after it was laid, so today I have gaps ranging from 0-5mm across the floor. I think it looks terrible, but I get many compliments on what a beautiful old-fashioned floor I have, so there's that. The important lesson there is that a board expands and contracts in width. If it's, say, 5%, then 5% of 70mm is 3.5mm in width, whereas 5% of 190 is 9.5mm...

Anyway, when everything was done with the foundation and the joists, I nailed a new suspended ceiling, taped the seams, and laid in new insulation, then added the new floor.

3. The Plastic: upon closer inspection, it wasn't as well laid as I thought, with numerous small holes where it had rubbed against sharp stones (probably already during laying), and I could see that in several places it had been laid over organic material. Off with the junk, clear out all sawdust and other debris underneath, add a bit more gravel at the worst spots, put in new plastic with better overlap and butyl sealing between the overlaps, also made sure it went up slightly against the foundation wall. I also laid a thin insulating mat (sold as "crawl space insulation" but delivered directly from the factory, and then I could see it was marked "concrete cover mat," the dealer admitted it was exactly the same).

Summary: all steps in order were: remove the old floor, empty all compartments of sawdust, dismantle the suspended ceiling, repair damages to the joists, clear away plastic and organic material from the foundation, add new plastic and insulation, nail new suspended ceiling, new insulation, new floor. All in all, somewhere around 40,000 SEK (year 2019 before the insane price increase during Covid) and at LEAST 250 hours of my life. Worth it.

Haha! Great! Thanks for the super reply, I hope that in total it doesn't exceed 100k in materials with air purifier, plastic, suspended ceiling, insulation, new joists, pine flooring, other wall surfaces, and moldings. It's about 43 square meters 😊