creaTing a warmer home
Work begins on insulating and drylining Ian Rock’s large new extension, while he turns his attention to specifying a wood stove
The last few weeks have witnessed a flurry of synchronised activity as work on the interior of our extension shifted up a gear.
This follows a fairly lengthy spell largely devoted to finding trades and obtaining quotes.
Deploying individual tradespeople is a bit like conducting an orchestra, albeit one resonating to the sound of power tools. Lots of individual contributions need to be coordinated in tune with the designer’s masterplan to ultimately create a harmonious three dimensional building, hopefully without too many bum notes.
insulaTing: a mammoTh Task
By far the biggest undertaking on the interior of our extension is the combined job of insulating, boarding, drylining and plastering — a mammoth task for which we appointed local plasterer Jamie Bosomworth. The first leg of this marathon requires accurate cutting and placing of 120mm-thick
Kingspan phenolic foam insulation boards between the rafters of all three main roof structures, taking care to first leave 20mm ventilation paths under the breather membrane. This is not an easy job at the best of times, particularly when it comes to insulating sloping ceilings at high level.
Prior to this, electricians Alex and Sam completed the first fix cabling within the scheduled three and a half day timeframe and were duly rewarded for their efforts by Mrs Rock bearing a steaming plate of hot sausage rolls (in addition, of course, to their agreed payment!). Electricians need to work closely with plasterers to coordinate all the various lighting points and switches, and I noticed that each electric cable had a reference marked on it in black felt pen to aid identification at second fix once engulfed behind acres of plasterboard.
After a week and a half working flat out, Jamie finished the first phase of insulating all the sloping ceilings. The key thing with insulation is not to leave gaps that moist air from the rooms can seep through and then condense in the cold spaces behind, so we made sure that any uneven edges were sealed with expanding foam.
The next job was to line the underside of the part-insulated ceilings with a vapour barrier sheet. Although the ventilation space retained above the insulation should, in theory, waft any humid air away, fitting a vapour control sheet is advisable as a ‘belt and braces’ precaution. To underline the importance of this, Jamie recounted a story about a damp problem he’d come across in a recently insulated roof. Apparently when he started hacking off the damp ceiling plaster a deluge of trapped water came dripping down — the result of ‘interstitial condensation’ caused by a lack of any vapour control layer to prevent humid air getting through.
We knew Jamie had other jobs rapidly piling up so it was agreed that he would return in two weeks’ time to commence the next phase.
choosing a woodburner
As with most big-ticket purchase decisions, choosing a woodburning stove involves a great deal of huffing and puffing, researching what seems to be an infinite variety of competing products. Splashing cash on desirable fittings for your new home extension should be a pleasurable pastime, yet making the right choice isn’t always straightforward.
What helped during our search for a woodburner was that we pretty much knew what we wanted — a sleek modern curved design in traditional black, with a decent-sized glass door to view the flames, an integral log store, plus the option of an external air supply, all within a price range of £600 to £900 (preferably British made). After what seemed like a lifetime scrutinising endless adverts and websites, and agonising over technical specifications we narrowed it down to one clear contender: the contemporary ‘Arctic’ stove range distributed by Greymetal. The only compromise was with my patriotic sensibilities as the stoves are imported from ABX in the Czech Republic.
Although the open plan ground floor space is pretty large, the stove shouldn’t have to work too hard because the primary warmth will be provided by underfloor heating. Also, the extension design exceeds thermal efficiency targets so heat retention should be very good. Woodburning stoves are renowned for belting out incredible amounts of heat and are actually most efficient when running close to peak capacity, so we opted for a relatively constrained 5kW stove. This also saves some weight at ‘only’ 110kg (compared to a backbreaking 170kg for the 8kW version).
Becoming so engrossed in choosing your stove means there’s a risk you can take your eye off the ball when it comes to the decidedly less sexy subject of specifying the correct type of flue that it connects to. Designing the flue route and calculating the various different component lengths, brackets and fixings takes a great deal of thought (and usually best left to your HETAS installer). It’s not always appreciated that the cost of buying all the flue materials can easily exceed the price of the stove, and the best prices I could find for these were from a company called Firebox. Because we’d used the Selkirk brand of 150mm twin wall flues for the initial lengths installed at roof level, we had to stick with the same manufacturer because different brands of nominally identical twin wall flues don’t inter-connect.
geTTing ready for The insTallaTion Before booking a firm date for a HETAS-registered heating engineer to install the flue and stove there were one or two outstanding jobs on my DIY list, such as trimming a couple of bedroom floor joists in the path of the flue to provide the necessary 50mm safety buffer (since our original design hadn’t allowed for a woodburning stove). Most stoves take their air for combustion from the room, so air vents need to be inserted in the main walls. This strikes me as slightly bonkers given all the trouble designers go to, to meet U value heat loss targets. Modern suspended ground floors with a ventilated void underneath can provide a useful source of air and it was an easy job to install the necessary ducting. This just left one small dilemma. The flue and stove need to be installed before the ceilings are plasterboarded but the ground floor is still a couple of months away from being insulated, screeded and tiled.
So to give the stove something to stand on, the section of floor directly underneath needed to be built up to the finished floor level and a suitable hearth constructed. It’s not unknown for promotional shots of stylish stoves in advertising material to inadvertently omit the non-combustible hearths required by Building Regulations, which obviously isn’t an option in the real world.
After briefly flirting with glass hearths we plumped for traditional creamy travertine stone, however it soon became apparent that if you don’t want to buy a roomful of the stuff, suppliers simply aren’t interested. On the off-chance I popped into the local showrooms of Stoneworld of Oxfordshire but it transpired that they didn’t have the product I wanted. Then, as I headed for the door, Rob, the affable proprietor to whom I’d been chatting, suddenly recalled that they had some small readymade-up display samples going begging. “These should do the trick,” he beamed benevolently.
nexT monTh: firsT fix plumbing
“spending cash on desirable fittings should be a pleasurable pastime, yet making the right choice isn’t always straightforward”