Timber vs PVC vs Aluminium?
PVC is more conductive than timber and also requires a hollow drip within the frame structure which allows air to circulate inside the frame further increasing heat loss.
With regards to aluminium it’s a whopping 2000x more conductive than timber! Hence why you often struggle to get a whole window thermal value (Uw) from an aluminium manufacturer and they concentrate instead on advertising the glass thermal value (Ug). There are thermally broken aluminium composites on the market, but they come with a considerable price tag. To save cost and retain performance most people seeking aluminium style windows go for aluclad timber instead.
Down the line when the units no longer perform as desired (generally due to misalignment or inadequate performance) PVC units can only be ripped out and disposed of whereas timber units can be realigned and upgraded. With new manufacturing techniques and highly durable polyurethane paints, timber units also require far less maintenance than ever before. Whilst aluminium offers the least misalignment possibility, there is no upgrade possibility on a unit which is often inherently poor performing to start.
PVC windows units have 10 times as much carbon embedded than timber units and limited recyclability. Non-recycled aluminium utilises a highly energy-intensive process to convert the raw mined bauxite but is fully recyclable providing it is not formed into a thermally broken composite.
A matter of preference, but most potential home purchasers further down the line will place a higher value on timber or aluminium over PVC windows. With architects clambering for slimmer and slimmer frames, aluminium has a very desirable aesthetic in modern design. A similar effect can be created by embedding timber frames in the plaster/render/cladding however, with reduced cost and higher performance.
A quality uPVC unit with comparable Uw values is not dissimilar in cost to a timber unit. There are however a lot of poor quality and low performing units out there at a considerably lower cost. Aluminium is the most expensive option, especially for the thermally broken specification. Aluclad adds around 30% to a timber model without sacrifice to performance.
How do I compare window companies?
1. Ensure you are comparing like for like estimates
Use the schedule from the first company to send out to the others to ensure that they are pricing exactly the same specification. A lot of companies keep their pricing document separate to the main schedule to make it nice and easy.
2. Compare whole window Uw value (not Ug value)
Ug only tells us about heat loss through the glazing and does not allow for the framing technology which is responsible for the vast majority of the heat loss. Remember the lower the Uw the better. Passive house units generally have a Uw of 0.6-08, standard triple glazing 0.8 -1 and double glazing 1.2-1.6. In comparison your old single glazed windows have a Uw of around 3 and sliding sashes 4.3.
3. Air tightness
Most companies undertake the testing, but few publish results on their website so you will likely have to request it. Its an important metric as it indicates the convective losses (i.e physical movement of air through gaps).
4. Lead Times
These vary widely, generally between 4 and 12 weeks. This may be of importance if you have to wait for an aperture to be created before measures can be submitted.
Check the small print not just the highly advertised number of years! i.e 10 years of virtually non existent cover is of little value.
6. Technical support
As well as providing technical product and installation information, a company should help you put together a schedule that optimises cost, aesthetic and performance and highlights where improvements can be made (reduction of openers etc).
What should be included in my window order?
Window estimates often look complicated and it can be hard to ascertain if they include everything you want and be sure that costs won't spiral at the last minute.
The following all generally have a cost associated so make sure they have been allowed for if required:
Toughened or obscured glass
Openers (this makes a huge difference to cost!)
Non standard finish, dual finish or aluclad
Trickle vents (we recommend taking a controlled ventilation strategy utilising systems like MVHR - contact us to find out more)
Who should install my windows?
You will generally have two options:
1) Your main contractor
If you are completing the install as part of a larger scope of works, this generally offers the best value and is the most straightforward approach as there is no difficulty in defining where the work is split between the window installer and the main contractor. Liability for product on site and the timing of the order is also simplified. Just remember to check your main contractor has experience in installing timber windows and ensure they are given a copy of the manufacturer's guidelines. We are happy to speak to or meet with the installer directly.
2) The window manufacturer's in-house, outsourced, or recommended contractor
Few window providers directly employ labour as demand for installation varies and they have lead times to maintain, but all should be able to recommend a company who has considerable experience of successfully installing their units or a company they regularly outsource to.
NB: Whoever installs the window needs to take responsibility for the final measurements as they would be the one required to ‘make good’ any mismeasurement.
How do you ensure a good window installation?
Aside from following manufacturers guidelines, we recommend using the Tremco Illbruck i3 installation system. Suitable for a wide range of window and doors (not just those supplied by Ecospheric) it enables a fantastic airtight seal to complement your high performance glazing. For more information, check out https://www.illbruck.com/en_GB/information/videos/
(Image source: https://www.youtube.com/watch?v=2d_g6NQjYXc&feature=youtu.be)
How do I minimise costs and maximise performance?
The majority of a window's heat loss is through the frame, therefore aiming for as close to a single fixed pane as possible is ideal. Cost also increases with complexity.
Option 1: Single fixed pane of glass
Option 2: 2 panes of glass (double the cost of option 1)
Option 3: 6 panes of glass (triple the cost of option 1)