The single biggest line item / expense in building a passive house is the choice of window supplier and system. As we all know window supplier have an historically poor reputation , when in Ireland at least, window sales men went door to door selling PVC windows in the 80s. Nonetheless, whenever you go to a trade show or building expo you are likely to be bombarded by science / facts / figures from the various companies who sell in your local market.
If there is one area where people are going to cut their cloth to measure when they choose to 'near passive' rather then passive , then windows is likely to be top of that chopping list. But, chop carefully. as to get PH certified or ever ‘ near passive’ means choosing very high performing windows - far beyond the capability of most window supplier....no matter what claims they make. I’ve included a few photos of what triple glazed windows look like to demonstate how very different they are.
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| Passive House window - looking from the inside out |
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| Width of central mullion is approx 160mm |
Quick summary of windows
- There are 3 components to the windows : the glazing, the frame & the spacer which separates the glass sheets inside the glazed panel.
- U values / numbers quoted by salesmen usually refer only to the thermal performance of a piece of glass not the overall window. Good quality spacers ( e.g. Swiss, thermix) and frames ( insulated , thermally broken, quality seals etc..) cost more than poorly engineered products or metal
- You obviously want both a manufacturer & installer who are likely to be in business in 5 or 10 years time lest window elements get damaged or need replacing
- Glass is the cheapest part of the window & the part that performs best thermally; frames are generally expensive & have worse U values.
- The PHI has a standards for window frame testing, those that pass this standardised test are said to be ' Passive House Certified'. There are also standard tests conducted by trade bodies, such as the British Fenestration Council (BFC) which are again a standardised approach rather than just a number. The two standards are not comparable & neither deals with the actual quality of the window or how well it will be installed; rather they deal with the thermal performance of the product.
- The importance & efficacy of triple glazing in a passive house cannot be underestimated; good quality windows eliminate draughts & temperature differences in a room.
- Some people will argue that in certain climates , in certain orientations that you can get away with high quality double glazing. This may be true in a minority of cases....but they are forgetting that one has to use the same frame as the triple glazing with double glazed glass panels; this negates most of the cost really.
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| The thickness of the window ca. 110mm...they are huge! |
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| Central Mullion again |
Sample key questions to ask:
- Do the windows & doors open in or out?
- How bulkly are the frames? Get specific dimensions & drawings!
- What are the materials available : aluclad( timber / aluminium skin on the outside), timber, PVC...How long have they been making each for?
- What is the spacer material?
- What are the various restrictions on open sections, e.g. Height vs width?
- What is the ironmongery range & what is their warranty?
- What quality of locks are supplied as standard?
- Are window locks & restrictors included?
- What are the treshold details around doors?
- Who so going to be responsible for airtighting up the the windows
- Who supplies window cills? Are they metal, plastic, concrete?
- Is a thermal calculation / therm on the proposed installation required?
- Is the warranty supllied from the manufacturer for the windows ex-factory or as installed?
- For non typical items such as patio doors, sliders, front doors, get specifics as the installation details
- What is tilt & turn, provide a demo of the mechanism?
- Multiple customer references, please?
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| Looking at a bottom hinged window from the inside |
To be honest, the above list just begins to scratch the surface of dozens of questions I'd have for any window supplier, but should get you started.
How to save money on windows?
- Consider installing yourself & possibly buying directly from the supplier ( most likely in Germany). This may have VAT implication as, in Ireland at least, supplied products incur 23% VAT whereas installed products incur 13.5% VAT
- Perhaps choose an older product from their product range which is not as bang up to date or has as modern a profile. Considering that you would like windows to last 20 years minimum then fashion today should really not be a driver.
- Cut out fancy extras like designer ironmongery or alarm contacts, the multiplier on each window is prohibitive – try to choose from the standard range
- Limit the number of open panes. On average an opening pane is a few hunderd Euros more than a fixed pane
- Cut down on central mullions & other decorative frame components.
- Whilst all such windows are made to order & you can technically choose any RAL colour, perhaps there are colours or finishes ( either internal or external ) which might be less expensive
- Bargain hard. & get at least 3 quotes & don't commit to anyone– you will be amazed at the variation in price
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| A passive house slider door - the mechanism is quite complicated to say the least! |
