“Contrary to my son’s description of a ‘timber box’, the extension is, to us, more of a treasure chest. He may joke about it, but it’s so much more than a ‘timber box’. It brings the whole house into the twenty first century, is very warm, extremely comfortable and has completely changed the way we live – allowing said son to run his business from home!” Those are the words of John and Susie Craig of Co Down who completed this unusual extension three years ago.

The architect’s brief was to provide an extension that contrasted yet complemented the existing house, made sense of the garage, utility room and dining space, created a better sense of arrival at the ‘back door’ as well as the southern aspect to the rear and to make the most of the views at first floor level.

“I had always noticed” John continued, “when retrieving balls or cleaning out the gutters, that the views from the garage roof of the hills and sea beyond were really quite special.”

The couple bought the mid ‘70’s constructed house in 1990 with the thought that four good sized bedrooms, full length living room, separate dining room and a large kitchen with a dining area and sun room leading off it, there would be no alterations necessary, unlike their previous three houses. However, as with many other families, working life has changed radically and that has resulted in one of their children running a business from home. In order to accommodate this change, the house layout required a reconfiguration and more space added.

The house is typical of its era, but John is a modernist at heart and had earlier investigated the possibility of a self-build in the garden of this large, 7/8 acre site. That was not an option as it is in very tightly regulated Greenbelt, so thoughts of a Huf Haus were shelved, but not entirely.

“Our first thoughts were to build the extension in the usual way with blocks and roughcast, the same as the existing house, but when I also added that it was essential for us to remain living in the house, the architect said that wouldn’t be possible. He then produced a model of what he had in mind, a timber frame pod that could be craned into position and we loved it. Years ago my parents bought an apartment in a large timber frame block and I’ve never forgotten how warm and comfortable they were, with minimal outlay on heating. A pre-fabricated structure meant a lot less mess and dirt on site which was really important too as we built it during the winter. I love this modern style and would have liked to change the whole exterior; I believe that designs should evolve and that architecture shouldn’t be of the past but rather look to the future, at the same time adopting new techniques and materials.”

Planning permission was granted in June 2008 without question, the only proviso being a second opinion from a structural engineer to check the foundations. The site is well screened by mature trees and hedges which help the ‘timber box’ to blend in and it’s not easy to see from the neighbouring houses. By November 2008 everything was in place and the house was sealed off at the kitchen to allow work to begin on the remodelling of the garage on the ground floor and extension on the first.

The rarely used large double garage was reduced to a single and the extra space turned into a TV lounge/living room. In order to support the timber extension above, a structural steel platform was inserted into the garage ceiling, allowing the timber frame first floor box to cantilever out over the entrance. A glazed corridor at first floor level links this new part to the existing upstairs rooms. All of the building work was insulated to well above Building Regulation requirements and a new window on the ground floor in place of the old garage door was made to match the existing multi paned ones. Finally, the extension was clad in Western Red Cedar.

Sustainable Building Modernist

As a ‘sustainable building modernist’, John had entertained thoughts of a grass roof on either side of the first floor glazed walkway. Practical considerations soon ruled that out when he began to think about maintenance, and solved the problem with a shopping trip to a large DIY store from where he returned with a roll of very convincing artificial grass! This looks good all year round and the only upkeep is sweeping off the accumulated leaves in the Autumn.

The Craig’s were fortunate that despite the substantial increase in habitable area, there was no need to upgrade the heating or hot water systems. They are still using the original oil boiler installed when the house was built and which was, according to the heating engineer consulted, “the best of its type and almost as efficient as any modern model.” The only change going through the whole house was the Craig’s decision to replace all the existing internal doors with new oak ones to match those in the extension, thus tying the whole house together.

Overall the project ran smoothly with very few problems, due in large measure John and Susie feel, to their previous experience of extending and by employing their architect to manage it.

“Our previous alterations gave us a lot of insight into just how much time it takes to do something like this and I knew I didn’t have that” John explained. “At the outset we actually interviewed the contractors who’d submitted tenders because we felt the relationship between them and our architect and us was crucial and if we all didn’t get on then things could only get worse on site. We also were very insistent on keeping to the budget we’d set and again, it was our architect’s job to fulfil that. If you do employ a project manager, don’t then go directly to the contractor when there’s a problem or something you want changed. That way leads to uncontrolled expenditure, you’re undermining the project manager’s authority and the contractor may also pull the wool over your eyes!

Living on site was definitely the right thing to do. The winter of 2009/10 was very wet and at one point rainwater was coming in where the original garage door had been and also into the kitchen – not good news at all! However the sealant was re-done and that proved successful. Had I not been living in the house I probably wouldn’t have seen it. Our main involvement was choosing the furnishings, especially the lighting. Using a combination of down lighters and task lighting you can radically alter your environment, something that wasn’t thought of at all in the 1970’s. We also took the opportunity to put in a lot of different types of low energy bulbs as well because when you work from home, good lighting, and lots of it, is very important.”

With their modern pod proving such a success, might John and Susie be tempted to self-build? “It’s certainly an idea and I must admit that we have thought about it” said John, “but I can’t help feeling that, after four extensions we’ve probably done as much as any self-builder – and possibly more!”

Original house size: 3,100sqft
Extension size: an additional 700sqft. In addition to the building work, the garage, utility room and breakfast area were refurbished.
Cost: £120,000 including project management and all fees.

Build Spec

Walls: Outer leaf of Western red cedar cladding, 50mm ventilated cavity formed with battens and counter battens on sheathing ply fixed to 150x38mm timber studs at 400mm centres to timber frame specification with 150mm Kingspan Thermawall insulation between studs. Air tight vapour control layer fixed to inside of timber frame with 12.5 plasterboard and finish to inside.
U value: 0.13 W/msqK
Other rendered walls at ground floor built using 300mm blockwork cavity wall with Warmfill ‘Supersilver’ bead insulation.
U value: 0.30 W/msqK.
Windows: Iroko wood double glazed with low E glass
U value: 1.6
Floors: 200mm joists as part of the timber frame construction with the cantilever supported on a steel frame hidden within the floor depth.
All floors filled with Rockwool quilt insulation between.
U value: 0.18 W/msqK
Roofs – Flat roofs: Sika Trocal SGmA single ply membrane waterproofing sheet on 185mm Rockwool Duorock insulation on 19mm plywood fixed to timber firrings cut to give required falls.
Roof structure generally 200 x 38mm joists as part of the timber frame construction, reduced to 122 x 50 at balconies to suit build up.
Areas for balconies have 50mm thick concrete paving flags by Acheson and Glover on HARMER slab support rings at corners of flags on top of Trocal protective fleece over the Trocal roof as elsewhere. Insulation at Balconies is Kingspan Thermaroof TR27.
Link corridor Zinc roof is standing seam in VM Zinc Plus at 5 degree pitch. Vapour control layers to warm side of construction and ceilings 12.5 plasterboard and finish to inside.
U value: 0.16 W/msqK