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 17 and 18: base render coat

Extension wall slurry coat  Existing wall slurry coat

The base render, or slurry coat to the existing walls and extension walls has now commenced. As well as providing a smooth substrate for the external wall insulation, this render coat also serves as our primary air barrier, highighted in blue in the section below.

wall section

Working between sub-zero temperatures (before Christmas) and the rain, the rendering is still ongoing, but having done the front of the property, our house is starting to take on a different look…

house metamorphosing

week 17: cavity wall insulation

CWI injection  CWI Injection at high level

The cavity wall insulation (CWI) has now gone in. Primarily, it will be the external wall insulation that will be providing the heat loss reduction and achieving our U-values of <0.14 W.m².K. However, in order for the external insulation to be effective, we need to fill the cavity as best as possible to minimise/eliminate air currents. Otherwise, warm air entering the cavity will rise out at the cavity head to atmosphere, bypassing the external wall insulation. The picture above right shows the insulation being injected above the ceiling line of the top floor (usually installations stop just above ceiling level). This is in order to reduce air currents all the way to the cavity head.

We have selected Platinum Ecobead as the CWI insulant. These are expanded polystyrene spheres that are injected at high pressure into the cavity – the manufacturer’s claim this totally fills the cavity, which is good. It is also blown with an adhesive, which means that the beads will stay in place, and not slump, when it dries. As we are replacing the windows and sills, a few days after the CWI installation, we get a unique opportunity to look inside the cavity to see how well the Ecobead has filled it. I am impressed!

viwew of cavity at window sill

sorry for the delay…

Dear readers – this blog is now quite behind due to problems updating the wordpress blog software. I am pleased to say, as of today, that the problem has now been fixed. The blog will be updated during the course of this week – so much has happened (and much more yet to happen). Please check back soon and thanks for your patience!

Ian

week 16: concrete gutters removed

At last! The gutters that have been causing the leaks in our house, via the cavity of the wall (see earlier post), have been removed. These took some grinding – three cuts needed to get them off and flush with the wall (see orange elements in drawing below). The plan now is to extend the rafters such that the roof overhangs the new external wall insulation and so that we can fit a conventional gutter system.

In addition to them having failed, these concrete gutters were one of the most significant thermal bridges in the house. As shown in the drawing below, we are planning to wrap external wall insulation across the top of the roof and link it to the loft insulation layer. This will significantly reduce the thermal bridging from the remaining elements of the concrete gutter system.

week 15: breakthrough preparations

 

The structural steel for the breakthrough to the extension from the existing hall was put in this week. The opening will be 2m wide, enough for access to the stairs down to the lower ground floor and to get to the studio on the ground floor.

With the cold weather now setting in, we decide that it is best to leave the masonry in place beneath the steel. We will need to remove at least the outer leaf shortly in order to close off the cavity prior to injecting the cavity wall insulation.

week 14: windows and doors arrive

 

The new triple-glazed windows arrived this week. Made in Lithuania, the EcoContract windows, sourced via the Green Building Store, arrived in-tact. They are still mostly in their packaging, so have only really checked the colour match is correct. But they look good, really good. The bi-folding doors (top left photo) weighs some 400kg and we will need to dismantle this before we can move it into place – more to follow.

week 14: intermediate floor starts

 

With the blockwork complete, the carpenters were able to make a start. The timber wall plate is bolted to the block using Hilti resin anchors to fix the M12 threaded rods into the blockwork. The joists are then attached to the timber plate using joist hangers. The same fixing method will happen on the existing wall. This approach helps to minimise air leakage. at intermediate floor level – often a key air leakage path.

The floor structure should be finished next week and will be temporarily boarded to give a platform from which to construct the roof.

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!