Rotten joist advice

[Tirglas_7]

Hi

Continuing on with my 80's dormer renovation I've discovered some rotten joists whilst pulling down a ceiling in the lower part of the house.

The house is built on a slope and the front door is on the 1st floor, accessed from a deck that juts out from the front of the house. The deck is suspended on joists. 1 third is over the lower hallway (which is where the problems lie) the remaining 2 thirds are the garage.

(the scaffold us not up anymore it's an old pic to show the house construction)

IMG_20170611_190000013_HDR

• Tirglas_7
• 2 Sep 2018

20180325_160758

• Tirglas_7
• 2 Sep 2018

When we purchased the house the previous deck, made up of some kind of mortar and tile construction was letting in water in numerous places. We had the deck replaced with an epdm flat roof with composite decking on a floating timber frame on top.

So the construction now is composite decking, epdm covering, 18mm osb, 25mm floorboards then the joists.

Problem is the company that did the work replaced some of the joists at the other end of the deck, but now I've found the other end all the joists are rotten to varying degrees. I obviously do not want to disturb any of the deck so I want to replace/repair the issue/damage.

I've been researching options and it looks like replacement, sistering or Bower beams plates could be an option.

Here are some pics to give an idea of the issues

This is the worst one, I can push a screwdriver through the top along the top approx 500mm

IMG_20180901_171524

• Tirglas_7
• 2 Sep 2018

IMG_20180901_171547

• Tirglas_7
• 2 Sep 2018

IMG_20180901_171552

• Tirglas_7
• 2 Sep 2018

These joists look terrible but are not soft,

IMG_20180901_171607

• Tirglas_7
• 2 Sep 2018

IMG_20180901_171759

• Tirglas_7
• 2 Sep 2018

This is the worst joist from below, its not square and is angled over, looking at the bricks and mortar at the end it looks like it may have been like that since installation? Should I remove and try and square it up? Or best left if it's doing its job (kind of)?

IMG_20180901_171540

• Tirglas_7
• 2 Sep 2018

This is the opposite ends, which continue on through to the garage, they're sat on a brick wall with the door to the garage going through

IMG_20180901_171622

• Tirglas_7
• 2 Sep 2018

IMG_20180901_171631

• Tirglas_7
• 2 Sep 2018

What is the best way of assessing the joists to see how much is needed to be cut out? I've been using a screwdriver to look for soft areas, all the end approx 100-150mm are soft, the rest of the joists don't look great but aren't soft. Is there a rule of thumb? IE if a screwdriver cannot be pushed through the timber its deemed OK? Or should I be looking to replace it all due to its appearance?

What is the best/easiest method to sort it all do that I'm not pulling the ceiling down or removing the deck in 5 years time?

Any other info or advice welcome, many thanks for taking the time to read my post

 

[John D v2.0]

They are rotten but are they damp?
If they have dried out they won't get any worse and they may well be enough for the span. They have glued the decking down which would add rigidity and the ceiling below would do the same.
I am in no way expert but first get a damp meter and make sure they have fully dried out everywhere, and then think about sistering or otherwise supporting the deck.

 

[Tirglas_7]

Hi John,

Thanks for the reply

Everything is dry, it's been watertight for over a year and we had 3 dehumidifiers running for a month down there.

I've just been down there again and tested with a sharp blade, although as pictured they dont look great they're mostly solid.

I've seen these BM17 Bower beams which allow for up to 17 inches of removed timber, they'll do the job on all but the worst one.

BM17 Bower Beams Joist Repair Plates (100mm X 1000mm) x 1 Pair Inc. 8 M10 x 40mm Coach Screw Fixings (DELIVERY TO MAINLAND UK ONLY) https://www.amazon.co.uk/dp/B0078L5XV0/ref=cm_sw_r_cp_apa_BXaJBbXRY3K14

One of the reviews however has a pic of a number of them installed to attach a longer length, not sure if this would be an option for me? Or if they're just incorrectly installed?

Screenshot_20180902-180334-01

• Tirglas_7
• 2 Sep 2018

There definitely more than 17 inches removed anyway.

Or should I be looking at other options for the longer repair?

 

[Tirglas_7]

going to replace all the ends with the BM17 bower beams, they are 1000mm and up to 17 inches can be removed, for the worst one i may replace the end then sister another joist next to it.

tooling wise whats going to be best to achieve a square cut on the in situ joist?

 

[John D v2.0]

You can get those mechanical reciprocating saws, that might do it. Anything circular would be very dangerous and a hand saw would take all week

 

[oldbutnotdead]

If you can lift the floorboards above then a circular saw will do it nicely (clamp a bit of batten to the joist as a guide for the saw to keep the cut vertical). Otherwise chainsaw would work (if you happen to have one) or reciprocating demolition saw thing (Lidl/Aldi have them in quite often). Don't even contemplate a circular saw blade on an angle grinder. Watch out for nails in the joists (worth having a look at the floorboards to see where the nails are)

 

[Tirglas_7]

Thanks for the advice guys

I can't lift anything from above due to the epdm roof.

I have a mini circular plunge saw which cuts to 25mm in depth, I was going to use that to start the cut, then finish with my reciprocating saw.

What's the concern with using a circular saw.? some kind of binding/kickback? Or just having to use a full size circular saw overhead?

 

[cdbe]

Jigsaw should do most of the way, my baseplate hits about 25mm in front of the blade, looks like you have battens between the joists and deck so you'd probably manage all but a few mm which could be finished with a hand saw. Recips tend to jump around quite a bit and produce a rough cut, especially above your head on a ladder.

Those beams aren't cheap. You could bolt timbers down each side the old fashioned way.

 

[oldbutnotdead]

Thanks for the advice guys

I can't lift anything from above due to the epdm roof.

I have a mini circular plunge saw which cuts to 25mm in depth, I was going to use that to start the cut, then finish with my reciprocating saw.

What's the concern with using a circular saw.? some kind of binding/kickback? Or just having to use a full size circular saw overhead?

Ahh, roof- awkward. A proper circular saw with guide etc would probably be OK (I've done the same but had full access to the timber). A freehand disc cutter would be a bit dicey.

You may run into bother trying to remove the rotten bits of joist (if the roofboards are screwed to the joists or even if they're spiked)- some bits of that timber may still be sound enough to make it a pain. Plus you've got no good way to fix the roofboards to the new bits of timber you're fishing in (probably not a disaster but not ideal.

I'd be very tempted to souse the rotted bits with magic juice (though as long as the new roof isn't leaking and there's airflow in that void they shouldn't get any worse), leave them in place and sister some new bits alongside them (coach screws or M10 stud would work)

 

[Tirglas_7]

Thanks guys,

Already purchased the bm17 plates, there's only a few quid difference between the larger and smaller ones so I went for the biggest.

I'd rather know its all solid as eventually
I want to replace the composite deck top with slabs on adjustable plastic posts like these

https://www.wallbarn.com/products/roof-and-terrace-finishes/asp-adjustable-support-pads/

The current deck looks terrible and as the neighbour has a sycamore attracts that green growth. Not one of the deck board ends has been cut straight and as they're attached to a floating deck the whole thing rebounds when first stepping on. The work was all done by the same company that left the joists in this state. I used to work away all the time so unfortunately my wife doesn't have the keenest eye to spot any issues!

But that's do far down the line Itll do for now until the rest of the house is done

 

[John D v2.0]

What's the concern with using a circular saw.? some kind of binding/kickback?

Yes basically. Circular saws are reasonably safe hen used on a stable surface at elbow height, anywhere where they could jump out think about how quickly the blade would stop and whether your other hand etc is in range. Any improvisation would bad idea and more than one member in here has had serious injuries from improvising circular saw blades.