First post, hello all!

We have bought a detached turn of the century, maybe a little younger, house that I am planning to to a deep refurb and try to follow enerPHit as closely as possible. I have an unlimited amount of questions and am hoping for advice !

My day job is building new houses so you may think this should be trivial but the more i read about passivhaus and enerphit the more it feels like im about to cross into a third dimension!

Couple of questions right off the bat that im mulling off the bat. Windows From what I have read its best practice to fit the window not onto part of the outer brick skin but completely in the cavity so it is surrounded by insulation.

Q1 Now bearing in mind window frames are 70-90mm wide How then in the front weather sealed when there is a gap ?

Q2. The sides of the window can be fixed with straps, which leaves it dangling in the air. What is there for it to sit on other than cavity wall quilt and a weak plastic cavity closer ?

Thanks in advance and i apologise already for the many many questiions that are coming...

Fred

There's also lots of threads on GBF about window mounting within the insulation for external wall insulation, where the window can only be supported from one side.

e.g.
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15771&page=1#Item_0

<blockquote><cite>Posted By: owlman</cite>Q1. If you use 3G the frame is quite likely to be more than 70-90mm

Q2. Depending on window type you may well have a cill detail much wider than the frame.</blockquote>

thanks for the reply cavity is 100 on the existing and 150 on the extension, will still need some sort of external sealing detail and something for the cill to sit on.

wonder what people use so it doesnt look shockingly bad.

<blockquote><cite>Posted By: Peter_in_Hungary</cite>Windows and doors should be part of the whole insulation strategy. What are the plans for wall insulation ? From your comments it sounds like CWI but CWI as a retro-fit can have problems depending upon the cavity and the insulation value won't be as good as EWI. Whilst EWI is much better than CWI there may be restrictions on fitting EWI

What is the width of the cavity vs. the width of the frames, this will affect the window fixing.

If the CWI has already been fitted then how well was it done. If done poorly then it may have little to no value.</blockquote>

EWI isnt an option (planning). Cavity has nothing in at present so will need to be blown fill from inside so as not to pepper the brickwork with holes. There is scope for IWI although space is at a premium.

thanks for the tips djh, im not good with tech.

The inside of the windows i get no problem, its the outside. Cant just tape windows to brick needs to be a decent finish that looks good ?

EWI - planning wont let us change conservation etc

Uk accredited details usually suggest you install the window so the frame bears on the exterior wall leaf. The frame is installed so that it bears on the outer leaf at the same time as partially bridging the wall cavity. I think the figures used to be a minimum of 30mm but more if the window frame permits. You need to check the minimum bearing specifications of the frame with the window manufacturer.

The sealing of the window can be done in a couple of ways. The way suggested by djh where you use an expanding tape which can be left as is as this provides the weather seal and then you use expanding foam around the frame to the inside of this as a secondary airtight seal. The other option is to use something like Soudal SWS system. This system uses a high modulus sealant to the exterior and is available in many different colours. This is then supplemented with an airtight foam to fill the gap around the window frame and then finally an interior acrylic airtight sealant. Personally I've tended to prefer the Soudal SWS system especially when working on my own.

Alternatively you can take either bricks or blocks and turn them so that they partially cross the cavity and use pir insulation board between this brick/block row and the inner leaf. Then bear the windows onto this level. But again the sealing of the windows to the outside can be the same as above.

You will end up with a brick reveal and then need to choose extended sills, or use a masonry stone sill which the window bears on. In my last cottage we hade the windows installed like this and the brick reveal was fine.

With retrofit there aren't the hard and fast rules. Rather it's finding a way that fits the existing building without too many compromises while reducing the thermal bridging as much as possible. It ain't gonna be perfect.

Posted By: djh

Posted By: djh(2) Have you run PHPP yet? What does it say about the necessary thickness of insulation?

How much does it cost to run something through PHPP?

Posted By: Doubting_ThomasThere's a 7-year-old thread here where someone was quoted a ridiculous amount for a PHPP energy assessment. The consensus back then was actually that around £2k maximum was sensible, or less than half of the average household gas bill in 2023, as another way to think about it!

It also depends what is included. Just running a finished design through PHPP, or multiple iterations to tweak all kinds of things until the client is happy and the design satisfies EnerPHit? Details of thermal bridges according to the PHPP inputs...? BTW: If you really want to go for EnerPHit, PHPP calculations are a requirement, more or less.

The architect I used for our extension & thermal upgrade had an 'options report' on offer (£ 1.5k ex VAT), which is PHPP based and listed the different measures needed to achieve various standards (AECB, EnerPHit, PH). This was money well spent as the outcomes have basically been my to-do list for the last few years.

More details of the existing building fabric and components would be help you get the best advice, e.g.

Internal decorative state etc.
Details of extensions or other major works being considered.
Windows, doors, floors, roof (existing make up, and state of repair).

I've done a (nearly finished) retrofit of a 1920s semi (all heating and hot water is gas, and for the year to June 2022 it was down to £83 for the gas, and £88 for the standing charge - family of four).

Some things you might consider:

Polyurethane foam cavity wall insulation (e.g. BASF Walltite, or Isothane Technitherm) - these have the best U value of any commercially available cavity wall insulation, and at the same time make a big improvement to both air tightness, and also deal with any cavity tie corrosion issues too. If you have 100mm cavities, you'll get reasonable results from this alone. Do it after you've fitted the windows, and take the opportunity to clear cavities as much as possible while you have the cavities open (e.g. building extension, or replacing windows).

A brick treatment like StormDry.

In my experience on this house, it was quicker and more effective to entirely replace a suspended timber floor with an insulated floating floor than to try and insulate it.

Spend a while digging through this forum, there's loads here.

Good luck!

Tim.