Using Landvac vacuum glazing in modern casement windows

[siggy_7]

Hello everyone. I've got some Landvac vacuum glazing units on order which I plan to fit into some new accoya windows for an extension I'm building. The rest of the property has relatively tired timber framed double glazing (stormproof casement style) and I plan to make and fit similar windows to those I'm going to be making for the extension to the rest of the house in the future. I've gone the vacuum glazing route partly because of the superior thermal performance even compared to triple glazing without having to go super-thick on the units and partly because I just like the high-tech nature of the product.

The query I have, particularly for those in the window making business, is whether it's necessary to get the Landvac units made into a thicker glazing unit (this is called Landvac Optimum (or hybrid), where the double glazed vacuum unit is used in place of a single outer pane of an otherwise conventional double glazing unit) or whether I can just fit the thinner (8.3mm unit thickness) units into the sashes. As the window design is a stormproof casement with friction stays and espagnolette openers, the sash will need to be relatively thick sectioned anyway, but I can accommodate this just by having a relatively shallow glazing rebate of say 25mm or so and a deeper inner frame section. The supplier mentioned that the hybrid units are made to achieve BS1279 compliance, without elaborating what this is and why making up the hybrid unit would help. Any pointers much appreciated. Thanks in advance!

 

[HOJ]

where the double glazed vacuum unit is used in place of a single outer pane of an otherwise conventional double glazing unit)

I don’t really understand your statement, could you clarify, are you dealing with a constraint, can’t be a listed building if the windows are storm-proof, having said that it could be, been there done that....

From my experience I have made some notes outlined as follows:

I made some windows last year, for a listed building, but used the Fineo glass units rather than Landvac, having had samples of both, client didn’t like the Landvac unit with the getter plug being visible.

The primary reason for our use of these units was to keep the size of the timber for the frames and casements as slim as possible, and to replicate the originals as close as possible, which were all single glazed. we only used these units as the only other option was the usual “slim” glass units, which in my opinion are a liability.

Another reason for the choice was the claimed acoustic performance as the property is on a busy town road.

I would suggest by using these particular glass units, in a standard, modern, storm-proof, stock size frame may look odd and be overwhelmed by the visual mass and effect of so much timber, along with the eye watering cost in comparison to a more readily available cheaper DGU, that if there is an issue, can easily be replaced, rather than, with the Landvac units, paying and waiting for a boat from China to arrive.

 

[siggy_7]

Hi, thanks for your reply. You are correct - I don't have any particular constraints. The building is relatively old (it's a countryside farmworker's house that was built in the 1850's and has been extended several times) but isn't listed or in a conservation area.

In terms of the Landvac Optimum units, you end up with three panes of glass - two are the Landvac unit, which goes on the outside, and the third is an additional pane on the inside face that is incorporated with a standard glazing spacer. So to make up a ~24mm unit for example, you would have a 4-0.3-4-12-4 unit using the normal system of specifying a unit thickness (I don't know if the convention is to write this outside to inside or inside to outside, apologies if I got this the wrong way around).

Our existing timber windows are stormproof double glazed, but old - the sashes are made of 45mm section timber and I think the glazing units are only around 16mm thick (into a 35mm frame rebate, 32mm sash rebate to provide clearance for a seal on the inner face of the window rebate). One of the main reasons for going the Landvac route is to avoid the very heavy sections you get with a modern triple glazed unit but still meet (well exceed) the thermal performance of a much bulkier triple glazing unit.

My preference is to just use the Landvac units without getting them made into the thicker Optimum units. If I stick with a 45mm sash thickness for strength and compatibility with friction stays and espagnolette locks (I'm making these myself so I have the freedom to make to any dimension on the proviso it works looks good and will be passed by Building Control), then I have 37mm of timber thickness split between the inner reveal and the glazing bead which feels like that would still look sensible cosmetically. I'm interested to know if anyone has made any windows like this, what issues I might encounter and if there are good reasons for going for a thicker unit.

 

[HOJ]

you end up with three panes of glass - two are the Landvac unit, which goes on the outside, and the third is an additional pane on the inside face that is incorporated with a standard glazing spacer. So to make up a ~24mm unit for example, you would have a 4-0.3-4-12-4 unit using the normal system of specifying a unit thickness

I understand now, haven’t come across these units.

In my reply post I mentioned I made some SP windows a few years ago, which were for a listed building, which made no sense when all the properties alongside had flush casements and sliding sash windows.

Anyway, we had to use the infamous 12mm slim units (CO insisted) so we kept the stock sections as slim a possible, however we didn't look at the option of using friction stays or MPL’s, because of the stock sizes, attached a PDF of one of my drawings, to show how I made them, if it’s any use:

 

[johnnyb]

The price and lead mean most folks haven't used vac glazing(me too) last I costed was woahh price! (That's even more than blimey price)
I saw some in an oak conservatory a spell back. I sniggered because the horse rosettes were all rattling on the walls such were the gaps! How do oak frames ever pass any airtight tests? The powers will insist on 7 inches of kingspan in the walls then pass draughty cowsheds with 80% glazing.

 

[HOJ]

last I costed was woahh price! (That's even more than blimey price)

Let alone the unit costs, fell off my chair when I saw the cost of delivery, the project I did work on came to a stop, because of the spiralling costs, as part of the project there was meant to be a lot of thermal and acoustic insulation upgrades, to make the replacement windows and the use of these glass units worthwhile.

 

[siggy_7]

The costs aren't cheap I'll grant you - I'm paying £290/m2 for the glazing, but in the grand scheme of things a £700 outlay for two windows (plus frames and hardware) isn't that big a deal, especially when I'm making the units rather than buying them in.

The section drawings were very useful HOJ, many thanks for sharing those - gives me confidence I'm along the right lines with what I'm thinking. I've had another look at my existing sashes today; they appear to still use the twin open-ended slot tenon type joints (looks a bit more like a finger joint at the tenon thickness to be honest) that are common in mass produced windows, and they have been here a long time, so I guess the sashes will still have plenty of strength and rigidity even at a 45mm thickness.

 

[Ollie78]

I am intrigued to see these actually used, I was just looking at the other ones called Fineo where they are actually glass welded together and claim the same thermal insulation as triple glazing in a 7mm unit. The 13mm plug on the landvac is too big for the project I am looking at. Be interested to see how annoying the mini dots are in practice or whether you just don`t notice them.