Help me choose some roof windows

[ProDave]

I have 2 roof windows to buy and fit very shortly.  Size 98cm tall, 78cm wide, both the same.

 

I am bewildered by choice.  I have come up with these 3 as a starting point:

Velux triple glazed, UW 1.0 £335 https://www.roofingsuperstore.co.uk/product/velux-ggl-mk04-2066-white-centre-pivot-window-triple-glaze-78-x-98cm.html

 

Basic Facro double glazed UW 1.2 £201 https://www.roofingsuperstore.co.uk/product/fakro-ftw-v-p205-white-painted-centre-pivot-window-78cm-x-98cm.html

 

Silly  money 4G Fakro UW 0.58 £867 https://www.roofingsuperstore.co.uk/product/fakro-ftw-v-p205-white-painted-centre-pivot-window-78cm-x-98cm.html

 

And there seem to be any number of different permutations, and not all of them even bother to list the UW values.

 

So stepping back a bit.  Each of these windows has an area of 0.7644 square metres.

 

It I take the worst one, UW = 1.2 W/m2K.  So at worst case delta t of 30 degrees, I get a heat loss from the window of 27.51 watts

 

Using my heat pump to make up that heat loss, with a typical COP of 3, means I will use 9.17W of electricity to make up that heat loss.  This will use 220Wh per day at a cost of 3.2 pence per day.  If I assume we get 100 such cold days in a year, the heat loss from one of these windows will cost me £3.20

 

Now the point of that ramble, is if I were to pay an extra £134 to get the triple glazed Velux the heat loss would reduce to 22.93 watts and annual cost of that heat loss to £2.70  So an extra outlay of £134 would save me 50p per year and thus take 268 years to save it's extra cost.

 

So my initial conclusion, is unless you really really NEED such a low U value (for certification) then with such a small window, there is no financial merit in buying anything other than the basic one?

 

Can anyone fault my argument or calculations and convince me to buy anything but the basic one?

 

 

[ProDave]

Update

 

I have just stumbled upon this one as my new bargain basement UW=1.2 offering, https://www.roofingsuperstore.co.uk/product/ptp-p205-white-upvc-centre-pivot-laminated-window-78cm-x-98cm.html

 

This has the attraction of not incorporating a trickle vent, which is something not needed with the MVHR anyway.  Something I thought (until I stumbled upon this) was hard to find.

[mike2016]

I was going to go fully passive house certified in which case I was lined up for the 4G Velux GGU MK08 @ €1062 + VAT each!  I need four of these and two smaller ones costing €8K all in. For 6 roof windows...!! They are the same width but 1.4meters long, rather than 1meter in your case. So, I think you got a good price! 

 

Never saw anyone take the approach to see what the extra heating cost would be. Interesting sums. A bit like Solar PV - what's the payback? It's not just heating costs though you might need to factor in. What about:

• noise - traffic - planes - rain - animals
• risk of overheating - g value options
• motorized vs manual
• easy to reach / clean
• blinds - manual vs motorized
• rain sensor - risk to indoor floors / walls if open during shower
• durability - how much grease or treatment is required for the basic vs more expense ones? 

I slept under a basic one in an attic for 8 years growing up so I know all about them!! Can't remember if it was single or double glazed. 

 

For the small addition of £134 I'd personally opt for triple glazing, a bit like business class on a red eye leg, it's worth the extra. But if your overall budget is tight, then it doesn't make sense, keep to the basic ones. I don't think you can add secondary glazing later so you are stuck with what you buy one way or another.....

 

The other thing is a good installer, familiar with the exact window manufacturer. If you're happy to take on this challenge brilliant, otherwise getting a product combined with an installer who is unfamiliar / not competent is not a combination I'd like to suffer. 

Edited August 28, 2019 by mike2016
installation issues to watch out for

[ProDave]

Both are on north facing roof, so solar gain is not going to be much of an issue.  Quiet road, so noise not an issue.  Rain noise, never been a problem in last house that has basic 2G roof windows.  Quite low down so easily reached to open.

 

At the moment I am leaning towards my new favourite without a ventilator.  I have not stumbled upon another that does not have that, and it is not a parameter you seem to be able to search for.

[mike2016]

It's a great price so I think you're onto a winner. 

[Ed Davies]

I did similar calculations on the capital cost of double- vs triple-glazed windows against the capital cost of the extra PV to replace the extra heat loss, taking into account the  approximately 1 hour- per-day generation you could expect from PV during the relevant months. It was all very marginal.

 

I decided on triple glazed for the four main-room windows (study, living room, kitchen (PK08) and bathroom (MK08)) and double glazed for the top-hung escape windows in the two bedrooms. The eye-watering cost of triple-glazed top-hung was definitely a factor.

 

The reason for triple-glazed on the main rooms, though, was the comfort of sitting close to them. Though the extra loss in watts for double glazed might be marginal the feeling of them perhaps “radiating cold” swung it.

 

Being able to get them without vents would have been the thing that could have perhaps swung me to switch to Fakro from Velux. I'm wondering if there's a good way of sealing them without causing any other harm.

[ProDave]

I keep looking at other windows in this size and I have not yet found another one with no vent.

 

One of these rooms is our en-suite shower room.  The other is the spare bedroom that is long and thin. It has another window on the end wall that deals with the means of escape so the roof window does not have to perform that role.  Neither room will be used for long sitting in front of the window stints.

[joth]

17 minutes ago, ProDave said:

I have just stumbled upon this one as my new bargain basement UW=0.2 offering, https://www.roofingsuperstore.co.uk/product/ptp-p205-white-upvc-centre-pivot-laminated-window-78cm-x-98cm.html

 

 

I think you mean Uw=1.2 

?

 

https://www.roofingsuperstore.co.uk/product/ptp-p205-white-upvc-centre-pivot-laminated-window-78cm-x-98cm.html

"This is a white uPVC double glazed window with laminated glazing and has a uValue of 1.2."

 

 

And If you need more options there's roofmaker too 

[ProDave]

1 minute ago, joth said:

 

I think you mean Uw=1.2 

?

 

https://www.roofingsuperstore.co.uk/product/ptp-p205-white-upvc-centre-pivot-laminated-window-78cm-x-98cm.html

"This is a white uPVC double glazed window with laminated glazing and has a uValue of 1.2."

 

 

And If you need more options there's roofmaker too 

Indeed, typo corrected. Thank you.

[AliG]

I have the velux centre pivot 3G windows.

 

One issue I have is that if they are high up or  above something you have to stretch over you cannot reach the handles which are right at the top, so I would watch for that.

 

I got them more for the noise reduction than U-Value.

 

Not having vents makes a big difference to that anyway.

 

I think you have nailed it, the only thing I might consider is the vents are useful if the windows are in an area prone to overheating, we use them in the windows in our games room which is in the roof and can get hot.

 

If you want more noise reduction and a better U-value I would consider the Fakro U6, most of the benefits of the U8 and not as crazy expensive.

 

https://www.roofingsuperstore.co.uk/product/fttw-u605-white-centre-pivot-triple-glazed-window-78cm-x-98cm.html

[the_r_sole]

.

Edited September 26, 2019 by the_r_sole

[PeterW]

Try Sterling Build

 

https://www.sterlingbuild.co.uk/product/rooflite-duro-apx-b700-white-pvc-centre-pivot-roof-window

 

 

[ProDave]

No danger of failing SAP

 

That Sterling build website is a LOT better, you get to see the U values in a simple search. Though for the same window they list a different U value.

 

A new parameter has been added, we now want a white painted finish, not UPVC so that's my cheap unventilated one struck off.

 

 

[ProDave]

Gosh this is getting complicated.

 

Just found this on a Facro description

Automatic air ventilation in all windows

Many manufacturers use a standard manually operated vent which is inefficient, causing unnecessary heat loss.The Fakro V40P automatic vent which is installed in Fakro pine roof windows is activated by changes in atmospheric pressure. It provides the optimum balance of fresh air regardless of weather conditions

 

So if I am reading that correctly, Facro have a vent you cannot completely shut off?

 

If so that rather rules them out for a (near) passive house doesn't it?

[ProDave]

So looking at this cheap one https://www.sterlingbuild.co.uk/product/rooflite-core-aax-b510-white-paint-centre-pivot-roof-window

 

The attraction is no trickle vent.  Of course it's an unknown male and poor U value.

 

WHY don't the good makes do one without a trickle vent?

[joth]

57 minutes ago, ProDave said:

57 minutes ago, ProDave said:

So looking at this cheap one https://www.sterlingbuild.co.uk/product/rooflite-core-aax-b510-white-paint-centre-pivot-roof-window

 

The attraction is no trickle vent.  Of course it's an unknown male and poor U value.

 

WHY don't the good makes do one without a trickle vent?

 

 

1 hour ago, ProDave said:

Gosh this is getting complicated.

 

Just found this on a Facro description

 

 

 

So if I am reading that correctly, Facro have a vent you cannot completely shut off?

 

If so that rather rules them out for a (near) passive house doesn't it?

 

 

Fakro FTT U8 certainly has no trickle vent

 

They'll also make a custom window too, for example they gave me a price for the U8 with z-wave opening (for example). Their website "chat" worked well to get this, and we exchanged emails too.

The custom spec didn't terribly increase the price (that's over the already pricy U8 price, mind)

 

Edited August 28, 2019 by joth

[andy]

Interesting - the U6 are also trickle-vent free, might see about a price for those with electric myself.

[ProDave]

3 minutes ago, joth said:

 

 

 

Fakro FTT U8 certainly has no trickle vent

 

They'll also make a custom window too, for example they gave me a price for the U8 with z-wave opening (for example). Their website "chat" worked well to get this, and we exchanged emails too.

The custom spec didn't terribly increase the procr (that's over the already pricy U8 price, mind)

 

Yes no doubt that is a VERY nice window.  But oh the price.   See my calculations in post #1. https://www.roofingsuperstore.co.uk/product/fttu-u805-thermo-white-centre-pivot-window-78cm-x-98cm.html

[joth]

22 minutes ago, ProDave said:

Yes no doubt that is a VERY nice window.  But oh the price.   See my calculations in post #1. https://www.roofingsuperstore.co.uk/product/fttu-u805-thermo-white-centre-pivot-window-78cm-x-98cm.html

To clarify I was meaning take whatever other window of theirs you do like the price of, and ask them if it can be custom made without the trickle vent. 

[dpmiller]

Personally I wouldn't panic about a vent being present...

 

have a look at the Keylite products too. We went for their UPVC units and they're very impressive, much handier to install than a Velux.

[ProDave]

1 hour ago, dpmiller said:

Personally I wouldn't panic about a vent being present...

 

have a look at the Keylite products too. We went for their UPVC units and they're very impressive, much handier to install than a Velux.

I would not panic about an ordinary vent, you can shut those. It was the Fakro making the statement I quoted above about having automatic vents that you cannot shut that I do not like the sound of.  And they don't seem to clearly state which windows have that automatic vent and which have a manual vent.  That sort of ambiguity puts me off choosing Fakro.  I will contact them and see how much they want for a window with guaranteed no vent.

 

SWMBO does not want UPVC, she wants white finished wood.  If she has accepted UPVC then I would be ordering that cheap, no vent, UPVC Fakro I linked to earlier.

[dpmiller]

they do white wood too.

[ProDave]

26 minutes ago, dpmiller said:

they do white wood too.

Link? I could not find it.

[dpmiller]

https://www.keyliteroofwindows.com/shop/centre-pivot-04-780x980mm/

[ProDave]

So the latest thinking is we like Fakro because the handle is at the bottom.

 

We don't like Fakro because they don't do the cheap no vent one in anything other than UPVC and we want white painted wood.

 

We don't like Fakro because the vented ones keep talking about this automatic vent that you can't shut off and you seem to have to pay a fortune to get any other with no vent.