With nearly 4,000 tiles now laid you can really appreciate the traditional dark red hue of the Rosemary clay tiles blending harmoniously with those on the main house.

There’s a definite skill in ‘matching the existing’; getting this right takes a great deal of care and planning. Nothing looks worse than a clumsy extension that was obviously supposed to blend in, but carelessly chosen materials ensure it stands out for all the wrong reasons.

red tiles on large extension

The tiles – nearly 4,000 of them – on the new extension have been picked to blend harmoniously with the existing house

A Flash of Genius

For the last few days, Anthony, our roofer, has been voicing concerns about one key detail — how to secure the flashings where the new roof slopes slot underneath the existing side gable roof on the main house. In theory, this should be a straightforward task using an angle grinder to cut a long groove under the verges of the old gable into which the new flashing could be wedged.

But, in practice, angle grinders can be hard to control. Even in experienced hands, blinded by copious clouds of dust, they have a nasty tendency to skid around leaving a crazed trail of unsightly scars. Club hammers and bolster chisels have also singularly failed to open up the desired gap. So we invited main contractor Godfrey over for a quick brainstorm.

The job was priced in full knowledge of this requirement so the onus to resolve this issue was on him, but other than suggesting partially rebuilding the existing roof, no one seemed to have a workable solution. Then I remembered a special cutting tool I’d come across when researching for the Haynes Period Property Manual — a machine called an allsaw.

tiled roof with flashing installed

The conservationists’ best-kept secret, the allsaw created the grooves for the new flashings to secure into

Primarily used by conservationists for excavating old lime mortar joints to delicately extract defective bricks, its twin rotating ‘feet’ should be just the thing for cutting a groove in the brickwork at the verges. 

Later that day, armed with the hired allsaw, brickie James clambered onto the freshly tiled roof and proceeded to cut a neat 5mm-wide line, perfect for inserting overlapping strips of Code 5 lead flashing. Half an hour later he emerged, job done, coated in a patina of red dust.

The lead flashing was then successfully fixed in place and draped down over the tiles. Pointing up the joint where the lead is tucked into the grooves is best done with special mastic as mortar can be prone to cracking, which is a common cause of leaks.

lead soakers fitted to tiles on roof of extension

Lead soakers were installed prior to the flashing

Finishing the Roof

With a complex roof design like ours there’s a lot of intricate detailing that’s essential to get right because botched junctions of all types are a major source of leaks. So roofer Anthony set about completing a few remaining details while complaining to anyone who would listen that he could do with an apprentice to help.

A lead saddle (used at ridge height at the junction between the new and old roof) was soon ‘bossed’ into shape using a special wooden mallet. This task was followed by installing strips of undercloak wedged under the gable end battens to perk them up slightly and keep rain from dripping off the roof edges.

Finally, the verges were pointed up with mortar in the traditional style. 

bossing of flashes on tiled roof

A bossing mallet finishes the job

A Visit from Building Control

The next day, building control were due to carry out their next site visit to inspect the main roof while the structure was still fully exposed. In preparation I gave head brickie, Daniel, a checklist of snagging items, such as fitting M12 bolts to roof collars and securing the wall plate straps.

When Andrew from building control showed up he seemed generally satisfied, stopping to check that sufficient lateral restraint straps had been fitted to tie the walls to the roof and floor structure, and that the wall plate straps were all screwed down.

I noticed him looking quizzically at a pair of stout props temporarily supporting the main rear roof slope, but I explained to him that the loadbearing studwall was due to be constructed the following week.

scaffolding on extension

Progress has been rapid on Ian’s 100m2 extension — with the main roof now finished and building control satisfied with the work thus far

Lean-to Roof  

Our extension design features a generously proportioned open plan ground floor which is about one-third larger than the space upstairs. This has been achieved without adding any great bulk to the building, thanks to a sizeable single-storey side addition. But construction of the mono-pitched ‘lean-to’ roof to this single-storey element couldn’t start until the scaffolding directly above had been moved.

rafters of an extension

The rafters for the lean-to cut timber roof were spaced at 400mm centres

Chippie Colin then set to work cutting and placing all the timber rafters for this cut roof, having first installed the missing loadbearing studwork upstairs in good time for the next building control inspection.

The rafters were spaced at 400mm centres in accordance with the approved drawings and engineer’s calculations, doubled up either side of the rooflights and a small integral flat roof. Internally, the sloping ceiling is designed to follow the underside of the rafters, incorporating the three rooflights to create an airy, light and spacious feel in the kitchen diner area.

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