Triple Glazing

[PeterW]

12 minutes ago, Oz07 said:

Yes I'm bored. Doesn't look as big a difference as you make it sound

Its not the same area though - Passiv is 1/5th of the 20p per metre, or the gap between those 20ps at the bottom.. 

[Oz07]

It is the same area that's why there's 5no 20p as opposed to 1no. 5p

[AliG]

I also have Rationel 3G windows. They seal extremely well. If noise is a concern I recommend laminated glass which adds a few percent to the cost and considerably reduces noise transmission.

 

As mentioned tough I would also focus on the airtightness as a lot of the noise actually comes in around the frames and absolutely having MVHR and no trickle vents. Our windows got considerably quieter when we put mastic around the window plasterboard junction on the inside.

 

If noise is a concern though I would also look at the design of the house as relates to wind. We have a couple of rooms with vaulted ceilings, they are considerably noisier when it is windy than the bedrooms with a loft above which are pretty much silent. Massive improvement on our old house though.

[SteveMack]

There are some discussions out there about triple glazing actually increasing noise if you get it wrong.  Something about making sure the 3 panes of glass are different thicknesses to ensure each one captures different wavelengths without passing them on.  You should probably opt for acoustic triple on anything facing the road, it uses a thicker piece of PVB in the laminated layer.

[newhome]

6 hours ago, jack said:

It may be that this particular BCO is giving them a break for whatever reason, but no way would I rely on opening a window for ventilation (and nor would I expect most BCOs to allow it). 

My BCO said that if the windows to the extension had what he called night ventilation then I wouldn’t need trickle vents. My old house had these and they were good as the window could be locked but slightly vented. Not as secure as a closed locked windows of course. 

[jack]

2 hours ago, newhome said:

My BCO said that if the windows to the extension had what he called night ventilation then I wouldn’t need trickle vents. My old house had these and they were good as the window could be locked but slightly vented. Not as secure as a closed locked windows of course. 

 

Interesting. I'm really surprised that building regs allow this, but I guess I've learned something!

[craig]

8 hours ago, jack said:

 

It may be that this particular BCO is giving them a break for whatever reason, but no way would I rely on opening a window for ventilation (and nor would I expect most BCOs to allow it). 

 

No in-room ventilation is even more concerning in a properly airtight house.

 

 

The regulations do not state you must have trickle vents, you must have a form of background ventilation and that "can" be buy opening the window for ventilation. It is down to how the regulations are interpreted by the BCO. 

 

11 hours ago, tonyshouse said:

windows are nearly last on the list 

 

They shouldn't be, the thermal envelope should always be number 1 on the list and that includes the windows.

Edited March 14, 2021 by craig

[tonyshouse]

I kind of agree but walls. Ceiling, floors come above windows as do draught proofing and air tightness 

[craig]

31 minutes ago, tonyshouse said:

I kind of agree but walls. Ceiling, floors come above windows as do draught proofing and air tightness 

 

There is still to this day details that come across my desk and I look at them and know instantly, that it has been the architects maybe even the clients last things on their mind. Windows and doors are integral to the thermal envelope and airtight layer. Without them, you just have a big hole in the wall(s) and airtight layer.

 

https://passipedia.org/planning/thermal_protection

[Gus Potter]

Has anyone seen some info on the net re tripple glazing regarding the life span of the sealed units (8 years?). There is some suggestion that the middle pane is in it's own greenhouse and subject to high temperature and higher thermal movement. Thus a tripple glazed unit is more prone to failure. We know they are more expensive, heavy to design for.

 

It may be that you need tripple glazing to get you over the line for BC purposes but if this is your forever home then is this a cause for concern? How much will it cost you to replace them (tripple glazed) at a later date?

 

@craig "Windows and doors are integral to the thermal envelope and airtight layer. Without them, you just have a big hole in the wall(s) and airtight layer. "

 

Yes Craig is bang on. Craig is taking a hollistic view. No point in putting in a Rolls Royce window if you neglect the detail around the window and let drafts fly about where they should not be.

 

 

[craig]

30 minutes ago, Gus Potter said:

There is some suggestion that the middle pane is in it's own greenhouse and subject to high temperature and higher thermal movement. Thus a tripple glazed unit is more prone to failure

It’s generally caused by thermal stress, it is reduced by toughening the glass on the middle pane but that also adds costs.

[Iceverge]

		Inprovement from Building regs
Airtightness	Before	7ACH		Gross Floor Area 150m2
	After	0.6ACH
MVHR	Before	0% Efficiency		2 story 12m x 7.5m footprint
	After	90% Efficiency
Triple Glazing	Before	1.2 W/m2 (Glazing)
(36.6m2)	After	0.5 W/m2 (Glazing)
Walls	Before	0.21 W/m2K
(210m2)	After	0.13 W/m2K
Roof	Before	0.16 W/m2K
(90m2)	After	0.086 W/m2K
Floor	Before	0.21 W/m2K
(90m2)	After	0.106 W/m2K
kWh/(m2/a)	W/m2
75/42		AT	AT/MV	AT/MV/3G	AT/MV/3G/W	AT/MV/3G/W/R
Airtightness	48/20	XXX	XXX	XXX	XXX	XXX
MVHR	60/37	33/16	XXX	XXX	XXX	XXX
Triple Glazing	68/39	40/18	25/13	XXX	XXX	XXX
Walls	68/39	40/18	25/13	18/11	XXX	XXX
Roof	72/41	45/19	30/15	22/12	15/10	XXX
Floor	73/41	45/20	30/15	23/13	16/10	13/9
	Annual Heating Cost (€)		(4c/kWh)
450	0	AT	AT/MV	AT/MV/3G	AT/MV/3G/W	AT/MV/3G/W/R
Airtightness	288	XXX	XXX	XXX	XXX	XXX
MVHR	360	198	XXX	XXX	XXX	XXX
Triple Glazing	408	240	150	XXX	XXX	XXX
Walls	408	240	150	108	XXX	XXX
Roof	432	270	180	132	90	XXX
Floor	438	270	180	138	96	78
	Annual Heating Cost		(8c/kWh)
900	0	AT	AT/MV	AT/MV/3G	AT/MV/3G/W	AT/MV/3G/W/R
Airtightness	576	XXX	XXX	XXX	XXX	XXX
MVHR	720	396	XXX	XXX	XXX	XXX
Triple Glazing	816	480	300	XXX	XXX	XXX
Walls	816	480	300	216	XXX	XXX
Roof	864	540	360	264	180	XXX
Floor	876	540	360	276	192	156
	Annual Heating Cost		(16c/kWh)
1800	0	AT	AT/MV	AT/MV/3G	AT/MV/3G/W	AT/MV/3G/W/R
Airtightness	1152	XXX	XXX	XXX	XXX	XXX
MVHR	1440	792	XXX	XXX	XXX	XXX
Triple Glazing	1632	960	600	XXX	XXX	XXX
Walls	1632	960	600	432	XXX	XXX
Roof	1728	1080	720	528	360	XXX
Floor	1752	1080	720	552	384	312

[Gus Potter]

Just now, craig said:

It’s generally caused by thermal stress, it is reduced by toughening the glass on the middle pane but that also adds costs.

Thank you Craig.

 

I'm more structures orientated, know a little about the principles of glass design but now know more.

 

Thanks again Craig. Every day is a school day.

 

 

 

 

[Iceverge]

Above is a spreadsheet from my energy planning. All figures taken from messing around with PHPP. Location is set to the South of Ireland. 

 

I used the backstop Irish values for my starting point and passivhaus with a small margin for the finish. 

 

Granted Airtightness may not be that bad to begin with.

 

I didn't bother changing the u value for the window frames so they're probably better than cheap double glazing. I also left the G factor at 3g for ease of calculation.  Glazing is split 58% S 16%W 16%E and 20%N. 

 

My main takeaways were:

1. The drastic effect of airtightness followed by MVHR and triple glazing. 

2. If your energy cost is very low there's little benefit in improving insulation beyond regs. (I know Ireland has tighter standards here than the UK)

 

In the first table the two figures are the total heat demand per year per meter and the second figure is the heating load. 

 

Note: These figures only work for one specific house in one location but should still give a general picture. If you live in a hotter or colder region or build a house of a drastically different shape the picture will be different. 

 

[Gus Potter]

4 minutes ago, Iceverge said:

 

		Inprovement from Building regs
Airtightness	Before	7ACH		Gross Floor Area 150m2
	After	0.6ACH
MVHR	Before	0% Efficiency		2 story 12m x 7.5m footprint
	After	90% Efficiency
Triple Glazing	Before	1.2 W/m2 (Glazing)
(36.6m2)	After	0.5 W/m2 (Glazing)
Walls	Before	0.21 W/m2K
(210m2)	After	0.13 W/m2K
Roof	Before	0.16 W/m2K
(90m2)	After	0.086 W/m2K
Floor	Before	0.21 W/m2K
(90m2)	After	0.106 W/m2K
kWh/(m2/a)	W/m2
75/42		AT	AT/MV	AT/MV/3G	AT/MV/3G/W	AT/MV/3G/W/R
Airtightness	48/20	XXX	XXX	XXX	XXX	XXX
MVHR	60/37	33/16	XXX	XXX	XXX	XXX
Triple Glazing	68/39	40/18	25/13	XXX	XXX	XXX
Walls	68/39	40/18	25/13	18/11	XXX	XXX
Roof	72/41	45/19	30/15	22/12	15/10	XXX
Floor	73/41	45/20	30/15	23/13	16/10	13/9
	Annual Heating Cost (€)		(4c/kWh)
450	0	AT	AT/MV	AT/MV/3G	AT/MV/3G/W	AT/MV/3G/W/R
Airtightness	288	XXX	XXX	XXX	XXX	XXX
MVHR	360	198	XXX	XXX	XXX	XXX
Triple Glazing	408	240	150	XXX	XXX	XXX
Walls	408	240	150	108	XXX	XXX
Roof	432	270	180	132	90	XXX
Floor	438	270	180	138	96	78
	Annual Heating Cost		(8c/kWh)
900	0	AT	AT/MV	AT/MV/3G	AT/MV/3G/W	AT/MV/3G/W/R
Airtightness	576	XXX	XXX	XXX	XXX	XXX
MVHR	720	396	XXX	XXX	XXX	XXX
Triple Glazing	816	480	300	XXX	XXX	XXX
Walls	816	480	300	216	XXX	XXX
Roof	864	540	360	264	180	XXX
Floor	876	540	360	276	192	156
	Annual Heating Cost		(16c/kWh)
1800	0	AT	AT/MV	AT/MV/3G	AT/MV/3G/W	AT/MV/3G/W/R
Airtightness	1152	XXX	XXX	XXX	XXX	XXX
MVHR	1440	792	XXX	XXX	XXX	XXX
Triple Glazing	1632	960	600	XXX	XXX	XXX
Walls	1632	960	600	432	XXX	XXX
Roof	1728	1080	720	528	360	XXX
Floor	1752	1080	720	552	384	312

 

 

Hiya Iceverge.

 

That is some impressive figures. I have copied a bit of your table below.

 

 

 

 

I,m not sure if I am right or wrong here but.. as a designer over the years I have found that the window market is a bit worse than the second hand car market. That's just me!

 

You may achieve these values with a very big area of glass and thus the exposed perimeter area of a frame is not that significant, you can see this effect when you look up the insultation required for a floor slab .. Kingspan / Cellotex ask you to calculate the area vs the perimeter.. and this principle in some ways applies to glass and the surrounding frame.

 

Now, with modern argon filled units say the heat loss through the window frame can have a significant impact on the performance. When chosing windows you need to consider this. But it's hard to compare like for like as for a manufacturer to test every combination of window size is very expensive.

 

While I think your figure looks good for the glass only, one needs to have an appreciation of what these figures mean in practice and how you can best apply them to your design.

 

@craigI think Craig may be able to expand on practicalities of this in terms of the detailing round the frame, exposing the frame externally less to the cold air. There is much more to this than just looking at the U value of the glass.

 

 

 

 

 

 

 

[Gus Potter]

16 minutes ago, Iceverge said:

Above is a spreadsheet from my energy planning. All figures taken from messing around with PHPP. Location is set to the South of Ireland. 

 

I used the backstop Irish values for my starting point and passivhaus with a small margin for the finish. 

 

Granted Airtightness may not be that bad to begin with.

 

I didn't bother changing the u value for the window frames so they're probably better than cheap double glazing. I also left the G factor at 3g for ease of calculation.  Glazing is split 58% S 16%W 16%E and 20%N. 

 

My main takeaways were:

1. The drastic effect of airtightness followed by MVHR and triple glazing. 

2. If your energy cost is very low there's little benefit in improving insulation beyond regs. (I know Ireland has tighter standards here than the UK)

 

In the first table the two figures are the total heat demand per year per meter and the second figure is the heating load. 

 

Note: These figures only work for one specific house in one location but should still give a general picture. If you live in a hotter or colder region or build a house of a drastically different shape the picture will be different. 

 

Iceverge,

 

I hope I have not put you off but I think that you could better spend money on making sure you get a good quality of build. By all means use your calculations as a target but the key will be the quality of the workmanship and attention to detail.

 

For example if you put up a timber kit that is soaking wet, then fill between the studs with PIR insulation. Leave it a few months and you'll find gaps between the studs and the insutaltion as the timber has shrunk. You'll also find that the PIR you thought was fitted tightly is moving about a bit. It now acts as a duvet with your leg out the side of the bed!

 

If you can get a handle on this type of behavoir and seal things up, look after the quality of the build and material then you can get a cracking job without resorting to more expensive materials.

 

 

[craig]

12 hours ago, Gus Potter said:

@craigI think Craig may be able to expand on practicalities of this in terms of the detailing round the frame, exposing the frame externally less to the cold air. There is much more to this than just looking at the U value of the glass.

 

There is and it is the part that is most overlooked. Devil is in the detail.

The first image is therm calc for the head, which the jambs were also the same, not the difference is value - the second is far more efficient than the first. The architect wanted the first option for a better flow of ventilation (this is a PH btw) and wanted the exact same on the jambs, we insisted on the detail change to second snapshot for the jambs. I'm waiting on the phpp update but it will be significant.

Picture 1

 

Picture 2

 

 

[Iceverge]

18 hours ago, Gus Potter said:

You may achieve these values with a very big area of glass and thus the exposed perimeter area of a frame is not that significant,

 For Clarity this is the overall improved overall window U value with glazing at 0.5 W/(m2K)

 

 This is when you drop to double glazing (1.2 W/(m2K) with the same passiv certified frames.Most double glazing frames would be worse. 

 

18 hours ago, Gus Potter said:

For example if you put up a timber kit that is soaking wet, then fill between the studs with PIR insulation. Leave it a few months and you'll find gaps between the studs and the insutaltion as the timber has shrunk. You'll also find that the PIR you thought was fitted tightly is moving about a bit. It now acts as a duvet with your leg out the side of the bed!

We didn't use any PIR as I think it's entirely overrated. EPS in the floors and walls and cellulose in the roof. Agreed, detailing is everything with low energy houses. 

 

 

6 hours ago, craig said:

The first image is therm calc for the head, which the jambs were also the same, not the difference is value - the second is far more efficient than the first. The architect wanted the first option for a better flow of ventilation (this is a PH btw) and wanted the exact same on the jambs, we insisted on the detail change to second snapshot for the jambs. I'm waiting on the phpp update but it will be significant.

 

I modelled all the junctions in our house myself. We compromised on some of the detailing such as placing the window at the outside of the cavities instead of the middle where they would have been most thermally efficient. It made it easier to build and secure a good wind-tight as well as an airtight envelope. Putting in a little extra insulation elsewhere to compensate was relatively cheap. 

 

I left plenty of fat in the overall design to account for shortfalls in the build process. ( I think i allowed for 1.5 ACH to reach 10w/m2 heating load) As it was we achieved 0.3 ACH50. We moved in 3 weeks ago and the house is performing well with only an intermittent 2kw rad for space heating. Hopefully when the house dries out properly we can do away with this other than in just the most extreme situations. 

 

On a large project or complex house shape chasing the gains made by ideal thermal detailing is certainly worthwhile. However my builder and I were first time passivehousers and the peace of mind granted by sticking close to known detailing and spending about €3k extra on insulation was the road we chose. As a result I suspect that as built performance will exceed 15kWh/m2a and 10W/m2. 

 

 

 

 

 

[Gus Potter]

Hi Craig and Iceverge and all.

 

Thanks for posting,  great stuff for me to see how folk innovate, approach design.

 

Can I ask what sofware are you using to model the window reveals? Is it a small package (spread sheet)  for just heat flow or are you using part of a big expensive Finite Element package like Abacus?

 

 

 

 

[craig]

@Gus Potter Our certifier/therm guy uses Flixo.