support for trimmers

[bluebaron]

HI, I'm planning on cutting through some joists for a loft stairs.

I've doubled up the joists either side of the hole and need to cut two back for trimmers.

I was planning on screwing the trimmers through the end joists using 3 x 100mmx5mm screws each end on each of two trimmers, i will also use a few 80mm screws to fix the trimmers together. However a mate said i should be using joist hangers.

Seems a bit overkill to me but anyone want to offer up any advice on the matter?

Ive attached a quick sketch below.

Thanks

 

[foxhole]

Either method should be fine.

 

[Ian H]

I'd screw and hanger if you can slide one under easy enough.

 

[Doggit]

If the screws aren't good quality, then they could shear so the joist hangers are more sensible. And it would be better to use coach bolts with square plate washers instead of screws on any of the doubled joists or trimmers.

 

[Deleted member 174758]

Twist nails, being softer than screws, are far less likely to shear when subjected to sudden (shock) loadings. That's why you use them in preference to screws on almost all occasions we use hangers. AFAIK building regs on new builds and extensions, etc require it as well (in other words if the work is subject to BCO or structural engineer sign off you may not get it with screws instead of twist nails). As Doggit says, the accepted way to sister joists, etc is to use coach bolts, preferably with star washers inserted between the timbers to reduce any tendency to move in service (and co-incidentally a pain to install in many cases)

 

[Doggit]

I gave up using the star washers a long time ago as they always pushed the joist appart (or can someone tell me the trick), and I didn't feel it was as secure a job.

 

[ajstoneservices]

Star washers = dog tooth connectors?

 

[bluebaron]

I was going against the hangers and was going to use 200mm screws from screw fix.

3 per joist (6 total) per end. Following advice above I may upgrade to the coach bolts but wary or splitting the timber as they are thicker.

This is what I was planning on using

http://www.screwfix.com/p/timber-tite-countersunk-joist-screws-green-6-5-x-200mm-10-pack/47271


These might be a bit thick for 50 x 140 joists

http://www.screwfix.com/p/turbocoach-coach-screws-yellow-zinc-plated-12-x-200mm-25-pack/3645g

 

[Doggit]

I've never understood why they are called dog tooth connectors; I'd hate to meet a dog with teeth like that.

You normally use M10 bolts, and you'd drill the holes first so that the bolts go through cleanly. I clamp the joists together before I drill, and that keep them more stable. The screwfix coach screws you're looking at are a replacement for coach bolts, but aren't really designed for the joist ends. But the turbo coach screws aren't suitable under any circumstances for what you're trying to do.

You're putting in loft stairs, but you've only got 140mm depth joists, so what exactly are you doing. This obviously isn't being done under a building control notice.

 

[Ian H]

You want more like:

http://www.screwfix.com/p/general-p...-bright-zinc-plated-m12-x-130mm-25-pack/64056

http://www.screwfix.com/p/galvanised-jiffy-hanger-270-x-100mm-10-pack/64910

http://www.screwfix.com/p/easyfix-s...-3-75-x-30mm-1kg-pack/12788?_requestid=452263

 

[bluebaron]

It's a loft staircase but not a loft!

I have a vaulted ceiling in my bedroom and then a normal ceiling above the ensuite and dressing room therefore a mezzanine level. This is for access to that level.

The joists only support the floor(no roof loading) and it's 6m wide by 3m deep with a wall halfway along dividing the rooms below. There won't be much weight up there really just storage.

 

[Doggit]

Definitely
Undoutably
Very questionable as you'd need at least 200mm nails to go through the double stringer first.

Well it's not being done under a building control notice, but you also aren't going for broke up there, but I think it would be remiss of me not to suggest you use the joist hangers and coach bolts. You're still transferring the weight and strength of two joists onto the outer two (albeit reinforced) joists, so if you're doing that part properly, why not do the whole job up to standard.

 

[bluebaron]

Thanks guys,

I went fur both then 200mn screws in the ends and hanger as well.
I'll finish with the twisted nails mentioned above.


Just for clarity it is all under building regs as the whole structure is new. The Mezzanine was an after thought as we thought it was dead space so we opened it up but didn't allow for access. the plan was to just use a ladder but now we want something more permanent hence the cut through.

 

[Doggit]

Stick a few more nails in the hangers, and you'll have a good belt and braces job there (otherwise it'll just be consider for show). Now what about the joists going from the trimmer.

 

[Ian H]

Looks good, exactly as I did mine but with a couple of extra screws