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.

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.

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


week 23: new garage roof

Garage roof stripped photo of complete roof to go here

The old garage roof covering had reached the end of its useful life sometime ago. Although not part of the thermal retrofit, we needed to replace it to allow the external wall insulation to be fitted onto the gable wall as shown below.

garage roof

The existing corrugated sheets are being replaced with a single ply deck. However, the existing structure only has joists at 1300mm centres, whereas they should be more like 600mm centres. The guys set them selves a target of removing the old roof, reinforcing the structure (including the replacement of some rotten joists) and getting the ply deck down in one day. Seems a tall order, but after a long, hard day, they manage it.

The new roof has the same Cefil membrane as our extension roof on the other side of the house (see earlier post). This is applied the following day and we’re back in the dry. Now, once we protect our nice new roof, we can get the scaffolding back so that we can render and insulate the gable wall above.

week 21: setting a new standard for flat roofs?

In my professional capacity, I do a lot of roof surveys, particularly roof failures on flat roofs. But, rarely have I actually specified one. So, I was naturally concerned that the flat roof design should be a good performer and wanted a good quality polymer waterproof layer (not the usual asphalt). Our contractor recommended Poole Single Ply Roofing Systems who use and install  Cefil UK membranes. Having seen a small sample and had a talk with the installers, I decide to go along with their enthusiastic recommendation.

Roof membrane applied  velux roof window

Installed on top of 150mm Kingspan TR26 insulation, the grey Cefil membrane is installed in a true craftsmanship style. It takes a little longer to install than I expected it would, but realise much of this additional time is due to the attention to detail around the Velux window up-stands and over the parapet. The final proof will be when the roof is complete, but if all flat roofs looked as good as this, I know that my defect survey bookings would be down! As the owner of this new roof, I have to say that this is a more re-assuring scenario.

This roof membrane will continue across our rear extension/balcony area and will replace the existing garage roof.

week 17 and 18: existing roof extended

rafter extension

The rafters to the existing pitched roof have been extended now that the concrete gutters have been removed. This will allow the roof to extend sufficiently in front of the external wall insulation. The Intello air barrier membrane beneath the rafters is Tescon taped to the existing timber wall plate to reduce the air leakage out of the cavity head (see drawing in previous post).

rafter insulation

We are also insulating between the rafters to provide insulation continuity between the external wall insulation and the loft insulation. The rigid insulation panels are squeezed tightly between the timbers and extend approx 0.5m above the (future) loft insulation. This means that they should also serve to provide a ventilation channel into the loft. This ventilation is necessary to remove any condensation from the cold loft space, and is often provided via proprietary ventilation channels.

New, matching roof tiles have been sourced. These will soon be fitted along with the new fascia and gutters – to be continued.

week 17 and 18: extension roof progresses

vapour barrier being laid

The vapour control layer to the new extension roof is now laid. The roof will be a warm roof construction, so the insulation will sit on top of the vapour control, followed by the final waterproof membrane. Before that, the roof light kerbs are cut in. The studio space below the roof will need very good natural daylight and we can’t fit windows along the long (party) wall. So, we are fitting three large roof lights instead.

rooflight kerb

The kerbs are flat pack units from Velux. Whilst they are fine for accommodating the Velux window units, they are not as well insulated as I would have expected. We will need to review the abutment of the kerb with roof insulation to see how we can add/improve the performance.

week 14: blockwork complete


With the scaffolding up, we were able to complete the blockwork walls this week. Despite the rain, the walls have still gone up quickly, albeit there has been a bit of extra re-pointing here and there to keep on top of the rain as it has washed the mortar away! The walls run to roof parapet height and will be externally insulated with the insulation continuing across the top of the parapet as shown in the detail below.

The insulation will start shortly, but in the meantime the priority is the internal floor followed by the roof so that we can get out of this mad weather as soon as possible!