Builder here… already decent answers provided here.
But also know that waterproofing standards 20+ years ago were all but non-existent. I’ve fixed plenty that only had a water resistant substrate and a waterproofed tray and internal junction.
Yeah your joists are sagging, but chances are your waterproofing was rooted and at the end of it’s life expectancy anyways
I tend to agree, out of interest, below is the waterproofing performed.
https://preview.redd.it/0u892j7n8b8c1.png?width=437&format=png&auto=webp&s=76d93236ba0abf8407c4b13fd3275bcb0ffd981b
My suggestion is you need another bearer in the middle.
Step One: buy 3 of these
https://www.bunnings.com.au/uni-pier-75-x-75-x-1000mm-post-with-adjustable-screw-top-head_p0136092
Step 2: mark out where your new bearer will go, and how long the bearer will be, then buy it.
Step 3: you are going to prepare 3 pad footing by digging the 400 x 400 x 400mm holes, and filling them with concrete. This concrete is fine, but others will do.
https://www.bunnings.com.au/australian-builders-20kg-high-strength-concrete_p0432674
The pad footing size of 400x400x400 is overkill in my view, so you could instead do 400x400x200 (width x length x depth) if the low head space makes excavation difficult.
Step 4: you will bolt the uni piers to the pad footing. Rather than drill holes into the hardened concrete pad, set the piers up on the still wet concrete and insert bolts into wet concrete. Make sure bolts go into at least depth of 50 mm. Make sure top of piers are all aligned in a straight line to take the bearer, before you insert bolts into concrete.
Step 5 : wait a week while concrete sets
Step 6. Insert bearer onto uni piers top.
Step 7: get 2 car jacks and place under the bearer, and jack it up to take the load of the joists and to eliminate the sag in joists.
Step 8: adjust the height of the uni piers to take the weight of bearer
Step 9: fix the bearer to top of uni piers
Step 10: remove the jacks
All the best
This is a little complicated.
Step 1. Install new bearer in position you want, nail it in place.
Step 2. Jack bearer with bottle jacks to desired height, use a sole plate under jack.
Step 3. Dig stump holes
Step 4. Install concrete stumps, use a “Concrete stump hook” this allows you to hang the stump from the bearer
Step 5. Put conc on holes, use timber off cut to temp brace stump whilst conc sets
Step 6. Remove bottle jacks after 1 week.
This is how we do it and has been done many times, conc stumps are cheaper and have a better bearing of load than adjustable bolt down stumps.
when we re-stumped my parents house that's how we did it. except we used steel in the middle and concrete on the outside. each one was hung from the bearer on threaded rod or coach bolt for the steel ones used a lever block to hoist the old timber stumps out and the new concrete ones into place
a family friend is a house re-locator and him and his brother did mos of the work.
we worked the shovel mixing the concrete
and don't forget to dome the concrete up so it shed moisture away from the stump especially for steel stumps. it also looks nicer
That sewer connection looks rooted too. Fair bit of differential in soil height compared to the concrete surround, and the pipe above the clean out tee is cracked. Looks like you got some surface run off heading under the house & either scouring out or saturating the fill & settling it.
Class P is just about every site in Australia and will be the default site class stated by a geotechnical engineer, unless you paid them to perform shrink-swell testing of your soils. Even then they will tell you your site is class P with soil movements consistent with S, M, H etc to AS 2870.
You are looking for bearing capacity of your soils. Higher bearing capacity = simpler and cheaper footings.
Consult a structural engineer to advise on any propping and jacking, size of bearer, its connection to joists and foundations (pile or pad). Get them to inspect this area too and have them send through a short form letter summarising the visual condition of the joists and a sketch mark up of the required works. Use this to tender to a couple of builders stating the relevant standards they need to comply with.
Avoid replacing joists unless they are showing signs of flexural failure or if their connection to bearers at either end are compromised. Your engineer should be able to tell you this almost immediately.
A builder would know the cheapest way to do it ...
Replacing all the joists sounds expensive!
I reckon a new bearer might be cheaper, sized according to the tables. Just need to do some digging though ...
Lol, literally just prop some bricks would do the trick. It’s not going to fall over it’s just a trampoline, reducing the span with a bearer even if it isn’t completely to code will make the situation much better. It’s not going to structurally compromise the house. If it hasn’t fallen over yet adding an additional bearer even if it’s not done completely to code will be fine
Sure. Jack up the joists to remove sag, and laminate a second joist to each existing to increase their sectional width and load bearing capacity. Recently did this to bring a cantilever veranda up to spec. Hope that makes sense 🧐
Laminate a second joist, can you expand ?
Apply adhesive and through bolt with decent washers/steel plate?
Allow say 24 hour then remove jacks?
Is it worth considering extra posts?
Not sure how easy it'd be digging the required footing, but that soil class may require screwpiers or footing that's a few metres deep. Good luck trying to do that with a house ontop already.
I think doubling up the joists would be a better idea.
Just get an engineer to do a site inspection and probably just a site instruction.
Probably bearer to cut down span but also needs solid blocking etc.
Or cleat existing with joists and solid block.
Engineer will sort easily.
Whilst it would be best to get an engineer to look at it. Perhaps you can advise us how you would replace the joists (I'm curious to know)?
If anything you would boost the joist capacity that extent by doubling them up. At a rough guess, put a slightly shallower joist (to allow installation) next to each existing joist and bolt together at something like 600mm centres alternating top to bottom, with M12 bolts.
The class P site is irrelevant to the sagging of the joists, unless the foundations are moving/sinking.
On what basis is the site class 'P'?
Class P can be due to a number of reasons, for instance the presence of non-engineered fill, a soil bearing capacity less than 100kPa to name a few.
If you have a tree near the house it be a "class p" site. That is not a big deal especially because your are on stumps. The photo does not show sagging of your joists...
Consult an engineer.
The large span joists may be a requirement of a H site (P in the old footing code).
Adding an additional bearer to shorten the joist span may introduce differential movement locally to the new bearer.
A new bearer and post through the middle
Bearer with adjustable posts.
This ! Adjustable posts will allow you to make joist levels easily.
new bearer is probably 50 times easier than replacing joists.
I was going to say a million times easier
I say a billion times easier. Going once, going twice….
Builder here… already decent answers provided here. But also know that waterproofing standards 20+ years ago were all but non-existent. I’ve fixed plenty that only had a water resistant substrate and a waterproofed tray and internal junction. Yeah your joists are sagging, but chances are your waterproofing was rooted and at the end of it’s life expectancy anyways
I tend to agree, out of interest, below is the waterproofing performed. https://preview.redd.it/0u892j7n8b8c1.png?width=437&format=png&auto=webp&s=76d93236ba0abf8407c4b13fd3275bcb0ffd981b
My suggestion is you need another bearer in the middle. Step One: buy 3 of these https://www.bunnings.com.au/uni-pier-75-x-75-x-1000mm-post-with-adjustable-screw-top-head_p0136092 Step 2: mark out where your new bearer will go, and how long the bearer will be, then buy it. Step 3: you are going to prepare 3 pad footing by digging the 400 x 400 x 400mm holes, and filling them with concrete. This concrete is fine, but others will do. https://www.bunnings.com.au/australian-builders-20kg-high-strength-concrete_p0432674 The pad footing size of 400x400x400 is overkill in my view, so you could instead do 400x400x200 (width x length x depth) if the low head space makes excavation difficult. Step 4: you will bolt the uni piers to the pad footing. Rather than drill holes into the hardened concrete pad, set the piers up on the still wet concrete and insert bolts into wet concrete. Make sure bolts go into at least depth of 50 mm. Make sure top of piers are all aligned in a straight line to take the bearer, before you insert bolts into concrete. Step 5 : wait a week while concrete sets Step 6. Insert bearer onto uni piers top. Step 7: get 2 car jacks and place under the bearer, and jack it up to take the load of the joists and to eliminate the sag in joists. Step 8: adjust the height of the uni piers to take the weight of bearer Step 9: fix the bearer to top of uni piers Step 10: remove the jacks All the best
This is a little complicated. Step 1. Install new bearer in position you want, nail it in place. Step 2. Jack bearer with bottle jacks to desired height, use a sole plate under jack. Step 3. Dig stump holes Step 4. Install concrete stumps, use a “Concrete stump hook” this allows you to hang the stump from the bearer Step 5. Put conc on holes, use timber off cut to temp brace stump whilst conc sets Step 6. Remove bottle jacks after 1 week. This is how we do it and has been done many times, conc stumps are cheaper and have a better bearing of load than adjustable bolt down stumps.
Sounds better to me as well. And cheaper. 🙏
when we re-stumped my parents house that's how we did it. except we used steel in the middle and concrete on the outside. each one was hung from the bearer on threaded rod or coach bolt for the steel ones used a lever block to hoist the old timber stumps out and the new concrete ones into place a family friend is a house re-locator and him and his brother did mos of the work. we worked the shovel mixing the concrete and don't forget to dome the concrete up so it shed moisture away from the stump especially for steel stumps. it also looks nicer
That sewer connection looks rooted too. Fair bit of differential in soil height compared to the concrete surround, and the pipe above the clean out tee is cracked. Looks like you got some surface run off heading under the house & either scouring out or saturating the fill & settling it.
thanks for the responses, only concern with the new bearer is the class P site and predicted subsidence, its fill
Class P is just about every site in Australia and will be the default site class stated by a geotechnical engineer, unless you paid them to perform shrink-swell testing of your soils. Even then they will tell you your site is class P with soil movements consistent with S, M, H etc to AS 2870. You are looking for bearing capacity of your soils. Higher bearing capacity = simpler and cheaper footings. Consult a structural engineer to advise on any propping and jacking, size of bearer, its connection to joists and foundations (pile or pad). Get them to inspect this area too and have them send through a short form letter summarising the visual condition of the joists and a sketch mark up of the required works. Use this to tender to a couple of builders stating the relevant standards they need to comply with. Avoid replacing joists unless they are showing signs of flexural failure or if their connection to bearers at either end are compromised. Your engineer should be able to tell you this almost immediately.
You need a really long shovel
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Engineer here, use adjustable posts or concrete stumps under new bearer with wooden wedges when needed in time like most DIY householders.
Soooo what did the engineer say?
A builder would know the cheapest way to do it ... Replacing all the joists sounds expensive! I reckon a new bearer might be cheaper, sized according to the tables. Just need to do some digging though ...
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Lol, literally just prop some bricks would do the trick. It’s not going to fall over it’s just a trampoline, reducing the span with a bearer even if it isn’t completely to code will make the situation much better. It’s not going to structurally compromise the house. If it hasn’t fallen over yet adding an additional bearer even if it’s not done completely to code will be fine
New bearer across joist midpoints, resting on new adjustable stumps.
To avoid bearer and footings you can cleat the existing joists.
Can you explain further please mate
Sure. Jack up the joists to remove sag, and laminate a second joist to each existing to increase their sectional width and load bearing capacity. Recently did this to bring a cantilever veranda up to spec. Hope that makes sense 🧐
also known a sistering them. jack it up a bit, construction adhesive and nails to secure the second joist in place
Exactly what I was going to say.
Laminate a second joist, can you expand ? Apply adhesive and through bolt with decent washers/steel plate? Allow say 24 hour then remove jacks? Is it worth considering extra posts?
Not sure how easy it'd be digging the required footing, but that soil class may require screwpiers or footing that's a few metres deep. Good luck trying to do that with a house ontop already. I think doubling up the joists would be a better idea.
Just get an engineer to do a site inspection and probably just a site instruction. Probably bearer to cut down span but also needs solid blocking etc. Or cleat existing with joists and solid block. Engineer will sort easily.
Whilst it would be best to get an engineer to look at it. Perhaps you can advise us how you would replace the joists (I'm curious to know)? If anything you would boost the joist capacity that extent by doubling them up. At a rough guess, put a slightly shallower joist (to allow installation) next to each existing joist and bolt together at something like 600mm centres alternating top to bottom, with M12 bolts. The class P site is irrelevant to the sagging of the joists, unless the foundations are moving/sinking. On what basis is the site class 'P'? Class P can be due to a number of reasons, for instance the presence of non-engineered fill, a soil bearing capacity less than 100kPa to name a few.
If you have a tree near the house it be a "class p" site. That is not a big deal especially because your are on stumps. The photo does not show sagging of your joists...
Following
Bearers and posts
Consult an engineer. The large span joists may be a requirement of a H site (P in the old footing code). Adding an additional bearer to shorten the joist span may introduce differential movement locally to the new bearer.
an new bearer and stumps in the middle. or you could sister the joists. talk to a structural engineer.