Levelling Joists

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Sheppy1972

7 posts

Wannabe Geek

#241058 9-Oct-2018 00:52

Hi. I'm in the process of replacing all of the floorboards in three bedrooms due to borer. The house was built in the 1920s, and the joists and bearers seem to be free of borer and in good condition. However, the house has settled over the years and there is a slope on the floor.

My question relates to a levelling technique that I've seen on YouTube, which seems to be common in the USA and UK. I believe it is called sistering joists. Basically all existing joists are left in place, but new joists are bolted onto them in parallel, such that the new joists are level. Is this technique allowed in NZ? Are there any cost effective alternatives that don't involve repiling the house?

Thanks for any advice.

Aredwood

3885 posts

Uber Geek

#2103617 9-Oct-2018 01:44

Re leveling the bearers sounds like less work than installing lots of new floor joists. And if the piles are Totara slabs, they will probably need replacing anyway.

And doing the job properly avoids issues with things like uneven ceiling heights, floors being higher than the bottom plates, height differences between rooms etc.

Although bolting on extra joists can still be a good method to compensate for sagging due to excessive spans.

Hammerer

2476 posts

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Lifetime subscriber

#2103620 9-Oct-2018 03:05

Legally, you probably aren't able to do this work yourself as foundation and subfloor framing have been restricted since 2012.

http://www.buildingguide.co.nz/construction/restricted-building-work/

Bung

6487 posts

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#2103622 9-Oct-2018 04:42

There is a difference between repairs to an existing building and new work.

For example the following wouldn't need a Building Consent and therefore wouldn't be restricted.

" Replacing old rotten wooden piles under a house with new treated timber
piles in the same positions, as long as the work is not complete or substantial
replacement"

That's not saying that an experienced builder shouldn't be involved.

nickb800

2719 posts

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#2103656 9-Oct-2018 08:24

Are the joists relatively straight (i.e. not sagging)? If so, I'd be looking to pack the bearers.

Here's a good guide, with good parameters to guide you (don't pack more than 100mm). There was a lot of debate around the use of jack and pack in Chch, however a lot of that related to insurance entitlements (does it return your home to 'as new' as defined in your insurance policy) and poor workmanship (not following the guide below). In general, it's a solid approach if done properly. It shouldn't be too awful a job if you good access while the floorboards are off.

https://www.building.govt.nz/about-building-performance/news-and-updates/codewords/codewords-issue-74/doing-it-right-with-jack-and-pack/

Fred99

13684 posts

Uber Geek

#2103731 9-Oct-2018 09:53

Hammerer:

Legally, you probably aren't able to do this work yourself as foundation and subfloor framing have been restricted since 2012.

http://www.buildingguide.co.nz/construction/restricted-building-work/

It gets a little bit tricky when it comes to repairs/maintenance.

I replaced 8 (out of total ~50) piles when doing EQ repairs on our house.

I contacted the local council to apply for official consent exemption for this work. Council responded with a request for more or less the same as would have been required for full consent, they wanted Geotech and engineered design - (overkill IMO - the piles were damaged because of a 1/10,000 year event). Replacing the piles was my choice - they could have been left as they were and packed the 10-35mm to relevel the floors. The new piles would have been to modern code / NZS 3604. The old piles were attached to bearers with #8 wire or nails. What was being done was "optional" and undoubtedly an "improvement" - but no...

I replied to Council explaining the above, and was stonewalled. I escalated that to the manager of the consents dept, and got a curious reply (now archived along with other documentation) stating that as the number of piles needing to be repaired was less than 20% of the total, I didn't need to apply for consent exemption as Council considered that in that case, the work was "already exempt". Problem was that my estimate of 8 piles was just that - an estimate. The other piles all seemed good, but until you detach the piles and lift the load, you can't really tell - there may have been more that 10 (=20%). With that explained - council then replied that so long as it was less than 12, it would still be ok to do the work without consent. But hey - that's 24% when they'd told me the limit was 20%.

I got my (LBP) builder to replace the piles. (legally I could have DIY). Access was good - was an easy job. They replaced 8 piles as expected, and included in the above they added straps (12 kN IIRC) to all post/bearer connections, bolted galvanised bar to all bearer joins etc. All good.

A couple of provisos:

I'd had engineers from my insurer and EQC look at the work and recommend a repair methodology. I didn't trust them - I paid for a structural engineer to do an inspection, checking areas of damage and repair methodology - with instruction to alert me if there was anything at all about what was proposed that caused concern.

Your home insurance policy will be void as soon as you remove or alter any structural support. The clause will be in your policy somewhere. It doesn't just mean that if you stuff up and your house falls down that you won't be covered - you've voided your policy, so won't have any cover for anything at all. You need building/construction insurance - many home insurers don't offer this, so you may need a policy from NZI or other. They will require details about the work - and if they aren't happy they won't offer cover. I suspect that if I'd stated that I was going to DIY rather than use an LBP, they wouldn't have covered it.

Fred99

13684 posts

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#2103738 9-Oct-2018 10:13

nickb800:

Here's a good guide, with good parameters to guide you (don't pack more than 100mm).

Just a note on that 100mm limit. Prior to the aftermath of the Chch quakes, the limit for packing bearers was 50mm.

MBIE released "revised" EQ repair guidelines in 2012, where they increased that limit to 100mm. At the time it was acknowledged that this was being done to be "less onerous to insurers".

Some packing (or notching) or bearers is/was normal, arguably jacking and packing a little to relevel restores things to "as (good as) new". Changing the rules the way that MBIE did - nope.

"Less onerous to insurers" of course, as that meant that many homes which were out of level by >50mm could now be repaired under the EQC / Fletcher EQR home repair programme as cost could be kept "under-cap" and not handed over to private insurers - who may be compelled by courts to do a more realistic "as (good as) new" repair - not retrospectively change the rules to suit.

EQC are governed by Act of Parliament - effectively above the law - you can't really sue them. Even in cases when they had High Court rule against them, they chose to ignore those rulings.

Bung

6487 posts

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#2103835 9-Oct-2018 11:15

I work on the "does it look right" principle. That usually means overdoing it. To me 100mm packing balanced on a pile is closer to being a ball bearing than a shim.

The house above us at the beach has been jacked 100mm at the edge with nothing really stopping the blocks spitting out. We could gain a 2nd floor 😊

Sharesies

Trade NZ and US shares and funds with Sharesies (affiliate link).

nickb800

2719 posts

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#2103867 9-Oct-2018 11:52

Bung: I work on the "does it look right" principle. That usually means overdoing it. To me 100mm packing balanced on a pile is closer to being a ball bearing than a shim.

The house above us at the beach has been jacked 100mm at the edge with nothing really stopping the blocks spitting out. We could gain a 2nd floor 😊

Not really an issue if you follow the guidelines. Assuming timber piles - you have skew nails holding the packer in, then straps attaching the bearer to the pile. Its obviously not sufficient for a lone pole to resist lateral forces, but when your piles, bearers and joists are well connected then you have a solid system.

Another good principle is leaving it better than it was before. It has been noted in several studies that older houses often have either insufficient pile-bearer connections or none at all - hence the EQC campaigns to check your foundations. Following the guidelines would be a substantial improvement

Fred99

13684 posts

Uber Geek

#2103883 9-Oct-2018 12:27

As well as arguably inadequate post/bearer connections, the bearer to perimeter foundation connections on our house were #8 wire embedded in the concrete, looped and attached to the bearers with 2 inch staples - as was normal back in the '60s. After the EQ, the staples were sitting on the ground. Not sure how far the house structure would have jumped off the foundation, would have had to straighten out any slack in the wire, then pull the staples completely out, so it must have jumped in the air at least several cm.

OTOH - and possibly due to good luck rather than careful design - the house stayed on the foundations - or I should say that after it flew in the air it landed back in about the same spot. We're probably about 2km as the crow flies from a strong motion detector that recorded peak ground acceleration of 2.2g (lateral) and 1.8g (vertical). I believe those are still the highest measurements ever made in an EQ - and the house survived (many didn't in this area) - albeit with considerable mainly non-structural damage.

Despite the poor original connections between posts/bearers - they didn't fail. The stuffed pile footings were pulled/rattled loose in the clay, but stayed together and continued to do their job.

I look forward (not) to the Alpine Fault letting rip. Was top of the mind when considering how to repair our house.

Lastman

306 posts

Ultimate Geek

#2103901 9-Oct-2018 13:19

Hammerer:
Legally, you probably aren't able to do this work yourself as foundation and subfloor framing have been restricted since 2012.

http://www.buildingguide.co.nz/construction/restricted-building-work/

You can do any restricted building work under the owner builder exemption subject to the normal requirement of any building consent..

Hammerer

2476 posts

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#2103910 9-Oct-2018 13:31

Lastman:
Hammerer:

Legally, you probably aren't able to do this work yourself as foundation and subfloor framing have been restricted since 2012.

http://www.buildingguide.co.nz/construction/restricted-building-work/

You can do any restricted building work under the owner builder exemption subject to the normal requirement of any building consent..

Yes. I overstepped the actual mark - I shouldn't post after midnight.

I should have said that legally he couldn't do the project in the way he envisaged it in his post:

https://www.building.govt.nz/projects-and-consents/planning-a-successful-build/scope-and-design/choosing-the-right-people-for-your-type-of-building-work/owner-builder-obligations/

You need to complete a statutory declaration form to show you meet the owner-builder criteria before you can use the exemption.

The form has to be witnessed and signed by a Justice of the Peace or someone else authorised to do so.

You will need to give the form to your local council when you submit your building consent application.

neb

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#2103928 9-Oct-2018 14:31

Sheppy1972: Hi. I'm in the process of replacing all of the floorboards in three bedrooms due to borer. The house was built in the 1920s, and the joists and bearers seem to be free of borer and in good condition.

Possibly unnecessary to mention this, but consider treating the wood with a solvent-based permethrin/cypermethrin solution to protect it from future borer infestation while you've got easy access to it.

Sheppy1972

7 posts

Wannabe Geek

#2104016 9-Oct-2018 16:34

Thanks for all the advice - it's much appreciated . Replies to some of the points made:

1. I agree with the comments stating that it would be far easier to pack and raise the bearers to level the floor. I guess the reason I was thinking about bolting on joists was that I was hoping it would not be classed as restricted building work if I didn't disturb the existing subframe, so that I could do the work myself. I assumed that packing the bearers would be considered more intrusive and hence would be more likely to need building consent.

2. The existing joists are pretty straight. I think I'd only need to lift them by about 20mm at one end of each room to level the floor, so it's not a huge amount.

3. Thanks for the advice about applying borer treatment to the existing subframe. I will definitely do this.

3. Thanks for all the links to building code regulations, particularly the one regarding building owner consent exemptions. I had no idea that there was such a provision, which would allow me to do almost any work on my own house, subject to the DIY work being listed on the LIM report.