Wall plate height for extension

[acurachris]

Hi

I am nearly ready to install my wall plate for the roof trusses which have been ordered. The truss manufacturer has been out and measured so hopefully everything is going to be correct there.

I asked the following question to the truss manufacturer (okay might be a stupid question).

Q. As my extension cavity is wider than the original house cavity, do I still lay the timber wall plate to the same height as the existing?

Their answer.

A. I can confirm that we would have allowed for the cavity being wider in the extension, and taken the wallplates as being the same height on the new as on the existing.


My questions.

What tolerance do I have? I'm confident i'll get the wall plate level and within a few mm of the existing height, or does the height need to be bang on?

Should the wall plate be laid on 10mm mortar just like the bricks/blocks?

I will need to strap the wall plate although it's to celcon lightweight blocks; is fastening these restraint straps into the blocks with standard wall plugs going to be good enough or should I use something else?

Sorry if these are basic questions! I'm a serial worrier!

Cheers, Chris

 

[Notch7]

I would have thought the external face of the wallplate would be the datum point to design a roof from.

 

[acurachris]

I would have thought the external face of the wallplate would be the datum point to design a roof from.

Sorry, what do you mean?

 

[^woody^]

The bottom chord of a truss is the ceiling joist, so if the ceilings are to be the same height, then so do the plates

 

[acurachris]

The bottom chord of a truss is the ceiling joist, so if the ceilings are to be the same height, then so do the plates

Yeah the ceilings are going to be the same height, I am more concerned with making sure the roof is level externally - old to new.

 

[23vc]

If your aiming for the external roof to match in to the existing, why are you trying to get the wall plate the same height as existing, as it’s likely to be different unless your existing roof is made of the exact same style of truss as the ones you’re fitting?
For the new trusses, the vertical measurement from top of truss plus lath and tile depth, down to the bottom of the ceiling tie/horizontal part of the truss, dictates the top of your new wall plate.
Sorry may have misunderstood what you’re asking but I had all this with mine and yeah it’s a head scratcher if you’ve not done it before.
Also, beware the existing roof being a bit wonky/saggy/ slightly different pitch front to back. I got mine pretty close but still had to nail some firrings on which got it bang on.

 

[acurachris]

unless your existing roof is made of the exact same style of truss as the ones you’re fitting?

The truss people have measured inside the loft and outside on extension so from their response I gather they have taken the existing trusses into consideration.

For the new trusses, the vertical measurement from top of truss plus lath and tile depth, down to the bottom of the ceiling tie/horizontal part of the truss, dictates the top of your new wall plate.

Did you measure your wall plate height once the trusses were onsite? Offered one up to the roof first?

I got mine pretty close but still had to nail some firrings on which got it bang on.

Did the truss manufacturer measure yours or did you do it yourself? How much were yours out in places, 5/10/20mm or more? Did you have to use firrings on all trusses?

Cheers, Chris

 

[23vc]

1) ok, if the truss manufactures have carried out a survey on site then I guess you should be good. I didn’t have that option.
2) yes
3) did it myself with drawings, trig, measurements. Truss guy insisted that I used some formula to “ensure it matched into existing roof” - glad I didn’t as it was way off and didn’t seem to take into account the existing roof wasn’t totally uniform, pitch was about 2 degrees different front to back.
My firrings were about 20mm down to nothing. Used them on all trusses, but they cost peanuts.

All that said, I’m still surprised that the wall plate height happens to match, when you think about the layout with the different width cavity wall, and the relative seat depths of new and old roof. I’d still try and knock up a drawing of your own or at least validate theirs.

 

[Leofric]

I’d still try and knock up a drawing of your own or at least validate theirs.

Yes, a section through the existing and a section through the proposed to show how it works at the eaves. Difficult to describe these things in words,they need drawing out.