fabric performance – thermography

front LHS2 IR

The fist thermal images of the finished house were taken very early in the morning at the end of January. The results are very encouraging and show, as expected, that the insulation measures are working well, and that we have significantly reduced the amount of thermal bridges, particularly for the concrete gutters. The image above shows our house in the foreground with our neighbours’ houses beyond. The temperatures of the outside of our house are the same as unheated surroundings: vehicles, plants, etc. Compared to neighbouring houses, not only are the surfaces cooler (less heat escaping), but the temperatures are more uniform, showing good insulation continuity.

front LHS IR

The image above was taken further up the street, with our house now in the background. Our neighbour’s house in the foreground has the same thermal properties as our house did when we moved in, i.e. no cavity wall insulation. The difference is quite striking between our properties.

rear IR

From the rear, the house appears to be performing well too. The wall insulation is continuous and the thermal bridging relating to the concrete gutters (as shown in an earlier post) have been eliminated. There is a small amount of thermal bridging around the new window frames, but this is expected given that we opted for less expensive windows that do not have thermal breaks in the core of the frame.

rear neighbour IR

By contrast, our neighbour’s house is losing more heat, as shown in the image above. The thermal bridges from the concrete gutters and the single leaf masonry panel beneath the windows are quite evident.

wemico trays

We have introduced some bridges that we hadn’t thought about. Ironically, it is from the steel trays that carry the external wall insulation panels that are conducting heat. These are fixed to the masonry (warm side of the insulation) and some of this heat is clearly coming through. Perhaps plastic trays would have been better. In the grand scheme of things, this is relatively minor stuff.

backblog #2: mvhr system commissioned

 Paul Novus300 Commissioning in progress

The heat recovery ventilation system has been running for some three months now. The system is a Paul Novus 300 unit, which has a heat recovery efficiency of up to 94%. The system commissioning included balancing the supply and extract air flows and setting the fan speeds for each setting. This all went well and the system balanced well (which isn’t always the case). The photo above left shows the ventilation unit set within a cupboard within my new office. With all the attenuators on the ductwork (see earlier post), and the sound insulation around the cupboard, the system is almost silent: audible only in boost mode.

The photo above right shows the commissioning taking place. The total air flow was measured and adjusted through the intake and exhaust terminals (outside) to ensure total design air flow was achieved. The internal terminals within each rooms are then measured, adjusted and-re-measured to ensure each room receives the right air flow.

More performance data will follow on future blog postings. Keep checking back.

backblog #1: loft insulation

I have been neglecting this blog and now have a backlog of stuff to update. So, resuming with the loft insulation (and ventilation ducts in the loft)…

Skip full of itchy stuff empty loft

The old glass fibre insulation was stripped out of the loft (lovely job), leaving only the original (pathetically thin) layer of granulated vermiculite insulation. I couldn’t see the point of removing this, so it was left in place. Once cleared and cleaned, the loft was ready for the MVHR duct installation.

Supply and extract risers boxings

The Lindab SAFE ducting is installed approx 200mm above the ceiling (100mm joist + 100mm tie beam). This puts the top of the 100mm ducts approximately at the top of the proposed insulation layer. As these ducts form part of the insulated envelope, I feel it is necessary to create MDF boxings, or shutters around the ducting to allow the insulation to envelop the ducts completely: 300mm to the sides and above, giving some 600mm of insulation to the loft in these areas. The photo above right shows an example of the boxings prior to the insulation.

Warmcel stack  blowing machine

We have used Warmcel for our loft insulation. This is 100% cellulose (recycled newspaper). A total of 85 bags have been installed using a blowing machine.

Warmcel installation

Finished insulation

The photo above shows the finished insulation, in and around the ventilation duct boxings. The boxings account for just over a third of the loft floor area and therefore the area-weighted U-value for the loft is now 0.10W/m².K, compared to 0.13W/m².K if the entire loft insulation was just 300mm deep.

opening for Bristol Green Doors


We have been busy with (the almost) finishing touches, just in time for the Bristol Green Doors event taking place this weekend (28th and 29th September). So if you’re in Bristol, please feel free to join one of our tours, which run at 1100, 1300 and 1500hrs on both days. We need to limit numbers, so please book – you can do so by leaving a comment on this posting.

More details about the finishing off soon, I promise!

green roof installation

Finished sedum roof

There has been a bit of a pause in the postings to this blog, mostly because we are busy decorating, which is a little boring to do, let alone write about. One thing that we have had done lately is the sedum roof over the extension and the porch.

The sedum layer has been laid by the original single-ply roofing installer, who now specialises in sedum and wild flower roofs. Before the sedum is laid, a geotextile membrane is laid on top of the water proof layer of the roof and the sedum drainage layer is placed on top as shown in the photo below. The drainage layer is made from recycled plastic and also contains a network of cups to store water and keep the sedum happy during dry weather. The organic substrate is applied on top of the drainage layer and the sedum is rolled out across this.

Drainage layer Substrate layer

The sedum was installed about three weeks ago now and has taken well (thanks to the break in the dry weather). The addition of the sedum roof should offer a number of benefits, which include: extending the roof life (less exposed to UV); reduce summer overheating in the studio space below; and reduce surface water run-off. Most of all it looks great.

reader’s request: more information on window fitting

I received a request for further information about how we fitted the windows to minimise thermal bridges. So here goes:

Window fitting stage 1

Each window unit has been fitted into an external structural timber frame, or sub-frame. The sub-frame is standard C16 grade timber and doesn’t need to be tanalised as it shouldn’t become wet within the insulation layer. The size of the timbers in this case were chosen to be 60mm deep for reasons outlined below. The first timber fitted is the sill piece to act as a ledger to support the window during positioning and alignment. The window unit is fixed back to the masonry using nail plates, but most of the weight of the window is on this ledger, so it must be a good fix. The other three sides of the sub-frame can then be fitted snugly around the window:

Window fitting stage 2 Window fitting stage 3

In our case, the surrounding masonry was treated with a slurry (sand/cement) render base coat, to act as the primary air barrier. So, once the windows were fitted and the render had dried, we could deal with the airtightness sealing – sealing the window to the sub-frame and the sub-frame to the wall, using proprietary air sealing tapes. In hindsight we made an minor error here. We should have taped the sub-frame to the masonry and then rendered over the top of the render layer tape (black tape).

We chose 60mm deep sub-frame because we were using 2 x 60mm layers of insulation. The thickness of the window frame is 78mm. So the idea was to have the first layer of insulation run into the side of the sub-frame and the second layer would fly across the face of the window frame by around 40mm as shown:

window detail

Again, with hindsight, we should have used sightly deeper timber for the sub-frame (say 70-75mm) to account for the 10-15mm adhesive layer for the first insulation sheet. This would have saved a bit of  ‘shaving’ on the second layer, which, of course is a slight thermal compromise too.

The picture below shows the first layer of insulation running into the sub-frame.

window insulation

I believe the principle we have adopted is one of the best ways of minimising thermal bridges between the window frame and the surrounding masonry. We could have gone one step further and used a structural insulation material for the sub-frame, such as CompaCFoam, manufactured in Austria, but I was put off a bit by the costs (around 10x cost of timber), and, as we haven’t gone for ultra-high spec, thermal break window frames (£££), I didn’t think it was a worthwhile investment in this case (investment greater than energy saving). But, it’s worth a look.

Hope this helps and would be interested to hear if others have adopted a different approach.

weeks 36 to 39: scaffolding comes down

Front of house

The big reveal…after an interminable wait for the scaffolding company, even to pick up the phone, they finally get them to come to take it down! But, it’s worth the wait. With the sweet chestnut cladding and steel Lindab gutters, the house looks great (completely unbiased opinion of course!). There is still a fair amount of finishing off to do: painting; render below DPC; roof profiles; sedum roof; etc., not to mention landscaping. Some of these works should be happening over the next couple of weeks.

Rear of house

The balcony is now usable. It is good and solid and almost thermal bridge free. The balustrade has been fitted: it looks okay, but not quite what we would have chosen (planning condition to match existing). Overall, though the rear of the house looks smart, and the rear extension, clad in the chestnut, smartly encloses the balcony at one end.

We haven’t quite decided on whether we should leave the chestnut to naturally silver, or whether we should lacquer it to retain the new-look colouring for as long as possible. The intention was to let it silver, but it’s nice as it is right now. I think we’re likely to leave it.

weeks 36 to 39: ventilation installation

MVHR in Pantry

We are fitting a balanced mechanical ventilation system with a heat recovery unit (MVHR). This is a ducted supply and extract system that removes moist air from wet rooms and supplies fresh air to living rooms and bedrooms. The heat energy in the extract air stream is recovered by the heat recovery unit and this is channelled into the supply air stream so that the heat energy is not lost. I evaluate many of these systems as part of my work and have found that there are frequently problems with the way the systems are designed, installed, or commissioned.. Often there are shortcomings on all three elements, – and the systems are getting bad press as a result. As we are beginning to build to increasing airtightness standards (and we are going fairly airtight here), we need a ventilation strategy that will deliver fresh air to satisfy the need for good indoor air quality. But, it is important to mitigate the resultant energy losses (extracting heated air) and use (power for fan) by employing an efficient ventilation system. If it can recover heat energy, then all the better.

I am keen to evaluate a system that has been well-designed, installed and commissioned – to monitor the system over a period of years and get some really good long-term data on the performance of an efficiently operated system. We have opted for a Paul Novus 300 unit, which is currently one of the most efficient MVHR systems on the market (94.4% heat recovery efficiency) and is certified by the Passivhaus Institut. Whilst the system can be efficient, the weak link in many systems is the ductwork that links all the outlets to the MVHR system. As the photo shows, we are using Lindab SAFE ducting, which is tubular steel ducting – not flexible plastic that many systems are. I am a firm believer that the ducting should be considered part of the long term fabric of the property – the MVHR may need replacing after, say 20 years, but I would hope to connect to the existing ducts when the time comes and not rip the house apart to replace that. The resistance in a rigid ducting system is also much, much lower, compared to flexible, meaning the system will move air much more efficiently and quietly.

MVHR isometric design drawing

The installation, designed in association with the Green Building Store, has commenced on the lower ground floor, and will need to be done in two or three phases (so more posts to follow). The MVHR unit itself is going into the existing kitchen, but we can only install this once we have moved out and into the new kitchen.

weeks 35 and 36: flooring

LGF flooring

The oak floor has now been installed on the lower ground floor. We use a local sanding specialist to both sand and oil the floor. At time of writing this post, the floor has only one coat of oil, but it looks really good. In the past I have hired floor sanders and got on with it myself, and was a bit sceptical on the advice that it should be done by a ‘professional’, but I was wrong. Knowing that the sanding company was doing the lower ground floor, I thought I would get them to do the hall on the ground floor too – a mixture of old flooring and new. The results were were astounding!

hall floor installation Hall sanding

First the hall floor was installed by the carpenters. We had the existing oak floor (made in early 1960s) re-profiled so that the extension in the hall matched. We were never sure how the old and new were going to blend in – until it was sanded…

old and new floor

The top half of the photo is the new floor, the bottom part of the photo is the existing floor – I thought it would look different, a little darker, but it is pretty much identical. It needs to be oiled next – that will be the acid test, I guess. I think I might get these guys to do the other floor boards in the house!


weeks 35 and 36: barge boards

old and new

When the rendering was done, the house looked clean and new. However, as we are keeping the existing roof, the original concrete barge caps made it all look a little drab at roof level. We came up with a solution to encapsulate the entire edge with a timber barge board that would fix into the existing concrete roof. It seems to have done the trick. The new barge boards tie-in with the new fascias for the guttering along the eaves and all of this timber edging to the roof will be painted the same colour as the windows.

bargeboard fitting