Green Building Store is now 21°

Swn-y-Nant, Shropshire

A newbuild house, designed using Passivhaus Planning Package (PHPP) software by Simmonds Mills architects and built by Ecovert Solutions has recently been completed for self-builder clients.

21°supplied the ULTRA triple glazed windows and doors and a PAUL Novus 300 MVHR heat recovery ventilation system for the project.


The clients were inspired by the Passivhaus standard for their self-build project but did not want to go for full certification. The house has a double height space which reduces the measured floor area that would make Passivhaus certification a bit more challenging. However, it was designed in PHPP by experienced Passivhaus designers Simmonds Mills and the project achieved an impressive airtightness of 0.5 air changes/ hour @ 50 Pa.

The house is built in masonry construction with 250mm EPS insulation added to the blockwork walls, which are finished with silicon render. The roof is Glulam beam with I-joists filled with 400mm Warmcel recycled cellulose insulation. The ground floor comprises 250mm EPS insulation and 200mm concrete with underfloor heating. Apart from the ground floor underfloor heating there are two towel rails on the first floor, all heated with a very small gas boiler.  There is a 300 litre hot water tank which can be heated from the gas boiler, but since the Solar PV panels were installed at the end of January, the solar has heated all the water via the electric immersion heater.

Triple glazed windows & doors

21°s ULTRA triple glazed timber windows and doors were specified for the project, with a whole window U value of 0.75 W/m2K. The inward opening tilt and turn window style was chosen alongside a selection of single and double fully-glazed doors, all finished inside and out in RAL 7015 paint finish.

The inward-opening windows frames were wrapped by the wall insulation and render which makes both the windows perform better and reduces maintenance as much of the frame is hidden.

Originally the clients had wanted alu-clad windows but were persuaded by 21° to choose timber windows instead. The ULTRA triple glazed windows and doors were chosen because they were well built with double compression seals for airtightness and because they were a reasonable price.

We are very glad we did choose timber windows as they were much easier to protect and clean during the building work from render over-spray etc. It is true that the timber windows are much easier to maintain and touch up than alu-clad windows would have been. We compared quotes from a few companies and the ULTRA range came out well and looked good. They are great. Visitors comment on the warmth, comfort and quietness of the house, which the windows and doors make a big contribution to. We love the evenness of temperature that Passivhaus design brings. In the summer we don’t want to fling the doors open that much as the house is so comfortable and is at the right temperature. Even with the hot summer we had the temperature in the house only reached 26 degrees on the odd occasion and now that people are turning on their central heating we are still at 23 degrees. We also really love our front door with the name of the house etched into it (Swn-y-Nant means the ‘sound of the stream’) and seeing its reflection on the floor in the afternoon. 21° were very accommodating in helping us get the obscure glass etched for this.


21°’s fitting team installed the windows and doors at the project.

We would really recommend that others use 21°’s fitting team. They did a great job and it reduced stress and potential problems on the self-build.


MVHR system

21° designed, supplied and commissioned the MVHR system for the project. A PAUL Novus 300 unit was specified along with rigid spiral-wound ducting.

We were really keen on having a MVHR ventilation system as we’d experienced similar systems in France and knew how well they deliver fresh air into houses. We love our MVHR system – it does exactly what you’d expect it to do. The house never gets stuffy, the air is always fresh and it is very quiet. We can only hear the system if we are in the utility room where the unit is located. We did experience a small ‘down-draught’ from the air valve in the sitting area with the double height space. 21° were brilliant, providing advice and assistance and then switching the air valve fitting for one that directed air into the room differently, which immediately solved the problem. Sometimes people comment that the air in Passivhaus homes is too dry but we find the humidity levels in the air in the house to be absolutely fine. We moved from Lancashire, so Shropshire is comparatively very dry! On the very rare occasions that the humidity in the house feels a bit too low we simply don’t press ‘Boost’ on our MVHR system after a shower and so add a bit of moisture into the air of the house.


Although undertaking a self-build was occasionally stressful, we have ended up with a beautiful house that we love. The architects and builders helped us realise our dream. The customer service and aftersales service from 21° has been excellent and has really helped our self-build project go smoothly. We wouldn’t hesitate to recommend them.


Project details


Simmonds Mills


Ecovert Solutions



Case study


Life changing homes