timber frame detail

Hi, calling the experts again please

attached sketch View media item 9557 details the area where bottom rail of an inner timber frame wall panel meets up with floor joists and wall plate at ground floor (outer block wall removed from clarity and I do not show the breather paper either)

what the sketch represents starting from bottom up is timber wall plate, two edge joists, locating plate, panel bottom rail, also shown is OSB cover plate on face of the joists as well as OSB boarding integral to the wall panel above it.

I have acquired this detail from a fairly recent 2 floor ‘commercial’ timber frame detail

My questions are for the one floor ‘stick build’ (i.e. making the wall panels myself) extension I am building

1) I have no problem fitting a locating plate but am wondering what the purpose of the locating plate is and for a self build is this normally fitted. What I am wondering is whether fitting panel bottom rails direct to edge joists or across ends of joists is another option and pros and cons

2) In the details I have found it looks as if the floor joist OSB cover plate does not cover the locator plate and therefore there is a gap in the OSB covering; is this normal and why or if not how else (I do not show the breather paper for clarity which would cover beyond the floor joist OSB cover plate)

Again thanks for any help please.

I can't see the need for those two double joists.

Typically, you would have a sole plate (say 4x1) and then the frame is fixed on this. That locater plate does seem a bit irrelevant, and s probably only there it take up any unevenness in the top of the double joists - in which case your "wall plate" is unnecessary

You have to determine where you timber frame is starting and wherever it is you should have it suitably covered by the breather membrane. And so if you are installing double joists as per the diagram, then the membrane will need to go to the bottom of them where it will lap over a DPC tray or suitable drip. Therefore you will need to fit the sheathing OSB over the joists and that locator plate - only for the purpose of forming a flush surface, nothing more.

There is no reason why you can't continue the inner wall up to the level of your locator plate, which will then become a sole plate and the frame can be fitted on top of that

In summary, that image you have is a poor detail

The detail that you have is for a suspended timber floor. The double joists are running parallel with the floor joists. On the other wall will be a single header joist and the joists will sit at right angles to it. Details vary on different buildings but most don't have a locator plate.

Thanks for excellent comments woody and stuart

yes I should have said it is for a suspended timber frame floor and it is one of the end walls and the other wall will have single header joist with joists at right angles exactly like stuart says. (was just easier me drawing the double joist end wall rather than the wall with joists at rt angles)

where stuart says most he has seen don’t have a locator plate do you normally see a joist cover plate that I detail either on ones that do have a locator plate or do not have a locator plate? (just checking whether this joist cover plate is common thing)

Also for ones with locator plate do you see the joist cover plate with the gap I am showing? And for ones without locator plate do you see the joist coverplate hard up against the panel osb ?

Woody where you mention ‘lap over tray or drip’ this is ground floor I’m thinking I just put the breather paper hanging loose a bit past the DPC strip in the inner brick wall under the panel exactly like you say but no no tray or drip is in the inner wall just a flat bit DPC ?? (ps said by a complete amateur ready to duck!)

Thanks again

Section in here for timber framing starting on page 100 http://www.sbsa.gov.uk/tech_handbooks/accred_details_2.pdf

Thanks ! (got to about page 30 and will try again in morning as my internet connection too s...l...o..w) got TRADA book which is v.good but some details missing for people like me..

It may be for a timber suspended floor but there is still no need for the double joists.

With that design, there will still need to be another joist next to the double ones, to support the floorboards (and the ceiling if a 1st floor)

A better design would be to take the wall up higher and do away with the double joists

With regards to the gap by the locator plate, then that is incorrect. The OSB should form a complete cover as a base for the membrane

You should try to prevent moisture wicking up behind the membrane, or other such potential of local condensation dampness just behind the bottom of where the membrane terminates. It may be OK if you just let it hang, or it may need a proper drip detail. Its just something to consider

The locator plate and double joist shown is more akin to SIPs construction, with the LP being the floor decking to the floor SIPs. No need to build it like that, as Woody says, for on-site construction: either build wall up to top of joist level, or extend studs down to a common plate level the same as the elevation where the joists span onto it.

Thanks everyone for help I like this site - given me some more to think about..

See what you are saying about building up or lower studs and have been thinking about his... If I did this OK for the wall panels parallel with the floor joists but for the wall panels on the other wall I’m thinking I would have to make the panels with a different individual height in order for joists to rest on this other wall and panels located on top OR use joist hangers at this wall to make same height panels;

Alternatively I’m thinking if i do as per my orig sketch (less locator plate don’t need it) then I can support the ends of the joists on above other wall AND build all panels with same individual heights up off the joists which I’m thinking would be easier for me to get everything square and at correct heights/less faff ? Alternatively if i saw some photos of different ways of doing it could just as easy chage my mind..!

…Another few hours with my slow Sketchup skills to weigh things up perhaps