Jump to content

House design: restrictions and solutions


Recommended Posts

OK, here's a further question, and yes I appreciate this is a sailing forum, but there's a large amount of other knowledge here.

Has anyone used thinnish (75mm) tilt slabs, poured onsite with fibreglass ties, stood them up as the ext. cladding, stuck insulating panels on the inside and then used that as one side of the formwork to then pour a structural wall (with the glass ties being used right through the internal form work)?

Kind of like the scheme below?

IMG_8674.thumb.jpg.53e496615001e23b82b688d326761082.jpg

 

 

 

Link to post
Share on other sites

Seems like an exspensive way to use tilt panels. Plenty of companies pour tilt slabs on site. Ward Neale was probably the best I came across in the Auckland area. Can't remember what company name he traded under. 

Not to sure about the fibreglass wall ties. All structures of the type you are proposing would need to be specific design by a NZ registered professional engineer, CPENZ or IPENZ registered. If within the Auckland region, council will require the engineer to be on their approved engineers register.

Would it not be better to have a 100mm tilt panel, then frame the inside with 150x45 timber frame which would allow for ample insulation and a still air space to run all the services. You would probably end up with less wall thickness.

 

 

Link to post
Share on other sites
9 hours ago, chariot said:

Would it not be better to have a 100mm tilt panel, then frame the inside with 150x45 timber frame which would allow for ample insulation and a still air space to run all the services. You would probably end up with less wall thickness.

 

Easier? Certainly. Cheaper? Likely. Desired interior/exterior finishes? No. 

 

Better? Certainly not. The whole point of using concrete is to have the thermal mass on the inside. Otherwise, why use concrete at all?

In the approach I propose above the tiltslab is saving on one side of the formwork costs - although you have to create it in the first place, and means you can have a board form exterior finish (or any other concrete finish you like) by planking under the tiltslab formwork. It's the finished exterior cladding. It's not load bearing, so the tiltslab itself would only need engineering to the level necessary to hold itself onto the wall ties and support it's own structural integrity. 

Other approaches for cladding would be brick in place of the tiltslab (but I don't like brick), strapped board and batten (see below) or to even do a double wall in situ pour - Boxing up the internal wall, followed by applying the insulation on the exterior face, between the ties that were already cast into the first wall, then boxing up the exterior and pouring that. But the risk of that approach is the possibility of a poor exterior finish (bubbles, poor vib etc.). Using the bottom surface of the tiltslab as the exterior face should mean you can more-or-less avoid bubbles and get a nicer surface, no? 

One could use strapping and weatherboards on the exterior, but the R-value penalty for strapping is considerable, meaning considerably thicker (more expensive) insulation. Additionally, you then need to fix the strapping to the concrete (additional fixings cost), add a vapour barrier etc, and you have to use a much higher grade of timber (and fixings) for cladding than you would for boxing. Finally, you have the additional longterm costs of maintaining (even painting or preserving) a wooden facade, and the considerably expected shorter life time. 

 

 

Link to post
Share on other sites
20 minutes ago, DrWatson said:

Easier? Certainly. Cheaper? Likely. Desired interior/exterior finishes? No. 

 

Better? Certainly not. The whole point of using concrete is to have the thermal mass on the inside. Otherwise, why use concrete at all?

In the approach I propose above the tiltslab is saving on one side of the formwork costs - although you have to create it in the first place, and means you can have a board form exterior finish (or any other concrete finish you like) by planking under the tiltslab formwork. It's the finished exterior cladding. It's not load bearing, so the tiltslab itself would only need engineering to the level necessary to hold itself onto the wall ties and support it's own structural integrity. 

Other approaches for cladding would be brick in place of the tiltslab (but I don't like brick), strapped board and batten (see below) or to even do a double wall in situ pour - Boxing up the internal wall, followed by applying the insulation on the exterior face, between the ties that were already cast into the first wall, then boxing up the exterior and pouring that. But the risk of that approach is the possibility of a poor exterior finish (bubbles, poor vib etc.). Using the bottom surface of the tiltslab as the exterior face should mean you can more-or-less avoid bubbles and get a nicer surface, no? 

One could use strapping and weatherboards on the exterior, but the R-value penalty for strapping is considerable, meaning considerably thicker (more expensive) insulation. Additionally, you then need to fix the strapping to the concrete (additional fixings cost), add a vapour barrier etc, and you have to use a much higher grade of timber (and fixings) for cladding than you would for boxing. Finally, you have the additional longterm costs of maintaining (even painting or preserving) a wooden facade, and the considerably expected shorter life time. 

 

 

No reason why it shouldn’t work.

But would suggest it would be cheaper to precast the whole unit off site, they call them sandwich panels. Or even onsite, rather that vertical form work. But your way minimises thermal bridging at the joins in the precast (not that I think it’s a problem in northern nz, but that’s just my opinion of course)

Link to post
Share on other sites

Can also use polyblock (polystyrene hollow stone block filled with concrete after you stack them) and plaster/render the inside and outside. Never seen it used like that, but have heard of it. Probably not quite what you want for the finish and thermal mass on the inside, although you can scrape off the poly on the inside before you plaster.

Edited by DaveNoy
Link to post
Share on other sites

If you frame on the inside of a solid mass like tilt panels you only have to  revert back to non solid constuction H1 calcs which would only require R1.9 minimum. With 145 deep frame you can bolster that number up and still achieve a still air space like what is used in easter europe.

I can see you are enjoying the design proccess. Just make sure your designer/architect is up to speed on all his documentation for all of the alterative solutions as this will save you a lot of time and money at the building consent application and proccessing stage. 

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...