Excessive cantilevering of roof joist

mywetpants · 29 Oct 2025

Hello

I just wanted some Internet advice on a cantilevered roof.

Pics will speak a million words, but Building Control have said the ends have been notched excessively at the end. The joist supports a warm roof deck.

They want remedial or justification for the work.

freddiemercurystwin · 29 Oct 2025

If they want justification then justification you will have to provide. They are excessive, they look to be much smaller than the fascia (or perhaps the photos are deceiving?) in which case why are they notched so much? I would hazard remedial work could include sistering say every third joist with one that's not been so excessively hacked about and then maybe a joist running along the whole length to link them all.

mywetpants · 29 Oct 2025

Basically what they’ve done is drill 2x6” to support the insulation/OSB for the warm deck. Giving a total 6” for the fascia and gutter

freddiemercurystwin · 29 Oct 2025

Not sure I follow, but the underside of the notch looks to be higher than the bottom of the fascia board?

mywetpants · 29 Oct 2025

It’s just the camera angle, I believe it is flush.

Engineer said it’s hard to justify based on the depth of the notching, and lack of foot traffic can’t be argued.

Remedial is to sister a joist or to remove the notch completely, losing the soffit.

freddiemercurystwin · 29 Oct 2025

As mentioned can just some of them be sistered rather than every one and why do the sister joists need to be as deep as the main joists? So you can still have a soffit, albeit with a deeper fascia.

mywetpants · 29 Oct 2025

That was what I was thinking, but the least destructive would be a corner bracket, or splice plate and restore the missing notch?

freddiemercurystwin · 29 Oct 2025

Can a 'corner bracket' (whatever that is) be justified by your SE? Surely to get a splice plate to work you would need to be able to push it into the (presumably non existent gap) between the top of the joists and the underside of the deck?

catlad · 29 Oct 2025

The reason he is probably quibbling is because those blocks haven't been filled in between the joists which would add plenty of support at the edge of the roof. Why have the grp trims been fitted before the insulation?

ToolboxTalks · 30 Oct 2025

Building Control may be right to flag the excessive notching. It can significantly weaken the cantilevered ends and compromise structural integrity. You’ll likely need an engineer’s assessment to justify it, with calculations or reinforcement details (like adding steel plates or sister joists). Without that, remedial work might be the only safe route.

Dereekoo · 30 Oct 2025

If by cantilevered roof you mean those 50 x 50 x 500 bits at the end then by assuming C24 timber and a total roof loading of 1kn/m2 and running the calcs then the BM/shear and and deflection are within permissible limits.

Engineer said it’s hard to justify based on the depth of the notching, and lack of foot traffic can’t be argued. What lack of foot traffic, can't understand this statement

freddiemercurystwin · 30 Oct 2025

He's clutching at straws with that statement, that's all.

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Excessive cantilevering of roof joist

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