Block & Beam for Timber Frame detail

[NickB]

I’m building a modern timber frame house.. not to passive house but as best as i can. We wanted to go insulated raft but our site is no good due to the very close hawthorn hedge and soil conditions to so we are going with block and beam. I have attached a very rough detail and wanted to get some thoughts before sending it to the engineer. We are planning on putting drainage in beneath the subfloor to ensure there are no issues there.

 

Does the Thermoblock location look ok where it is, just below the frame? It feels like there will still be bridging through the block-work beneath it.

Thanks!

[Russell griffiths]

Have you had this from somewhere or just having a scribble yourself ?

looks a bit odd to me, 

why is it all balanced on one 100mm block 

whats the engineering brick for 

what do you mean by 140mm concrete block, 140mm wide or high, if wide how is that balanced on 100mm wide engineering brick. 

 

It might be that the drawing is just badly scaled, as it doesn’t add up to me. 

 

Would normally be larger blockwork under the block n beam with marmox block on top. 

So larger at footing coming up and getting thinner not the other way around. 

 

You are also also going to have a large over hang with the cladding, you could step the frame in and have external insulation over the outside. 

 

Your frame also sits very high, so there is little insulation from outside to inside if you draw a diagonal line through the drawing. 

 

Draw it up without the periscope vent as this is deceiving the picture by not showing the other row of blocks that will sit where the vent is. 

Edited August 2, 2020 by Russell griffiths

[NickB]

Thanks for taking a look. It's just a rough sketch I have done that i want to get right before sending it to the engineer tomorrow (it is to scale though yes), as they won't be looking at insulation, but more the structural side.

 

My issue is we have a height restriction and i don't want to raise the internal floor too high as we will have to lose room height. The DPC has to i believe be 150mm above ground level, which means the frame has to sit roughly where it is i think other wide the frame would be pushed down a course. I have made a few changes, but it requires a vast amount of the Marmox which will be quite expensive so would be good to get any thoughts. 

Ive made some tweaks here. How does this look to you?

 

Edited August 2, 2020 by NickB

[Reiver]

10 minutes ago, NickB said:

My issue is we have a height restriction and I don't want to raise the internal floor too high as we will have to lose room height.

 

 

I had the same problem in my draft design, and hence am looking at the Springvale Beamshield system which puts the insulation between and underneath the beams rather than on top. Not quite sorted yet (should get final pricing next week), but promises a U value of 0.12 with a P/A of 0.55

[NickB]

Ahh that sounds really interesting, i'll take a look at that now. Have you worked out any detail drawings yet on how it might work?

[NickB]

Any idea how can you avoid cold bridging through the ends of the exposed beams and into the screed with the Beamshield system?

[Reiver]

14 minutes ago, NickB said:

Ahh that sounds really interesting, i'll take a look at that now. Have you worked out any detail drawings yet on how it might work?

I'll try and dig them out later on, they're ont' other computer - mine's with Isotex ICF though so there's 125mm concrete on the inside of the insulation, a bit different from timber frame.

[Reiver]

23 minutes ago, NickB said:

Any idea how can you avoid cold bridging through the ends of the exposed beams and into the screed with the Beamshield system?

You mean around the perimeter? I did a quick analysis of the thermal resistances in the Beamshield Plus system and it is the insulation under the beams that does most of the work - hence you essentially have "warm beams".

Edited August 2, 2020 by Reiver

[NickB]

Yeah, i mean the the ends of the beams around the perimeter... if you had ufh it would travel through the screed and the beams to the ends which in my case would be exposed to the world. I suppose if you had a cavity filled with insulation it would be ok but with my timber frame i can’t see how it would work. 

[Reiver]

I put Marmox blocks level with the under beam part of the insulation: 

[Reiver]

32 minutes ago, NickB said:

Yeah, i mean the the ends of the beams around the perimeter... if you had ufh it would travel through the screed and the beams to the ends which in my case would be exposed to the world. I suppose if you had a cavity filled with insulation it would be ok but with my timber frame i can’t see how it would work. 

Since your poured foundations look nice and wide, could you build double walls with insulation between just up to the base of the timber frame?

[Russell griffiths]

The beams do not go out to the outside, that video shows cavity construction. 

With solid construction or timberframe your beams sit 100mm on top of 215 blocks so only halfway. 

 

@NickB flip your two blocks from the footings over so they are flat, then just one marmox block. 

 

See what hat that looks like. 

 

 

Edited August 2, 2020 by Russell griffiths

[NickB]

Ahh I think I see. More like this?

 

 

Edited August 2, 2020 by NickB

[Russell griffiths]

Then add external insulation from dpc down to the ground and that will improve insulation and remove that horrible 100mm step  out you have, either render this or brick slips or cement board or upvc plank, something that is good with being in contact with the ground. 

Lots on here have all used different things to cover theirs, anything but wood. 

[Nickfromwales]

I'd add a vertical rip of 25mm thick  PIR at the screed perimeter too, so you're less exposed at the periphery of the heated floor, eg so just the plasterboard sits atop the screed, rather than the service batten & plasterboard.

[NickB]

Thats super helpful Russell as i was looking into doing something like that but wasn't sure it would work with brick slips etc. Great to know people have done it. Does this look ok?

 

Just added the 25mm rip too.

 

Edited August 2, 2020 by NickB

[NickB]

Where would you put a Radon barrier? Just where the DPC is or just in place of the DPC to replace it?

[Nickfromwales]

Don't forget the insect / vermin stainless mesh under that additional external insulation

[NickB]

Ok i’ll add that. How do you ventilate the wall cavity well with that insulation there?

[Mr Punter]

You cannot close off the base of the cavity.  If you want insulation down to the ground make it 25mm thick so as not to impede the flow of air through the vertical battens.

[NickB]

Ok thanks, i’ll do that

[Russell griffiths]

Cut the top of the external insulation at an angle so any moisture that comes down the cavity sheds outwards, this provides a gap for ventilation, step the insulation in a bit so to add some interesting details, just not the 100mm you had or it will look like a council house that’s had external insulation added. 

 

Loads of little things need adding to finalise this but thats a robust design to work with. 

[CC45]

@NickB Interesting thread here - Once its finalised could you upload it?  Looking to improve what we've done this time in the next one....

[NickB]

Yes of course i’ll do that.. i’ll do it in sketchup tomorrow before sending it to the engineer to check it all out.

[NickB]

I had to make some amendments to accommodate the drop in height for the garage. Do these look ok with the wall sitting on the floor like this.