Breathable retrofit & old-house insulation · Sparrowholt, the Halse marshes & the conservation districts · Est. 2014
An old wall is still breathing. Insulate it that way.
Breathline retrofits pre-1930 houses with wood fibre, lime and sheep’s wool — materials that let vapour out instead of trapping it in. Every project starts with a moisture survey, ends with wall sensors left in place for a year, and lands somewhere between them that a plastic-bodied insulation could not reach without risking the fabric of the building.
Since 2014
The practice, in figures
Services
The four breathable systems
01
Dense-packed wood fibre — walls
Stud and frame walls filled through small borings with blown wood fibre, density-matched to the build-up so no cavity is left to convect. Vapour-open by nature, treated borate against anything that chews, and the fabric keeps drying outward the way it has for a century. Holes plugged with lime mortar, not caulk.
02
Wood-fibre sarking board — roofs
Insulated sarking over the rafters, lime-parge beneath, and a breather membrane specified to the exposure of your particular roof pitch. The room-in-the-roof stops being the coldest room in the house without becoming a sealed box that sweats behind the purlins every February.
03
Internal linings — cork & wood fibre
For walls that cannot be touched outside: calcium-silicate or cork board bonded direct to the masonry, wicking and warm, with lime plaster over. The wall keeps drying inward through the lining — the system listed buildings officers actually write back about, and we handle the consent drawings.
04
Sheep’s wool & draught-proofing — floors & lofts
Suspended timber floors lifted board by board, wool between the joists, and the boards returned with the grain matched. Lofts get wool to 300 mm with eaves-vent kept clear by design. The unglamorous layer that makes every layer above it honest — the draughts that vanish here are the ones the survey measures.
Moisture, monitored
The sensors stay for a year
A breathable retrofit is a claim about physics, so we instrument the claim: temperature and relative-humidity sensors set into the wall build-up at the survey, read remotely, and reported to you at three, six and twelve months against the model. If a build-up is drying toward the safe band on schedule, the letter says so in a line. If anything drifts, it says that too — a full year before it could ever become a stain.
Dry verdict, or we make it dry
If the twelve-month readings show a build-up we specified holding moisture outside the safe band, the rework is ours: new materials, new labour, new sensors, no invoice. It has been needed twice in eleven years — one lime render over an unbonded oxide, one blocked chimney driving rain sideways — and both walls now read drier than their models.
Sparrowholt & the marshes, 2025 — 2026
Houses breathing easier
Six retrofits from last season, photographed at the twelve-month sensor reading. Captions name the system and what the walls did — the only review an old house can write.
How it runs
Survey to second spring
The order is chosen by physics — draughts, floor, walls, roof — and the sensors that go in at the survey stay until the second spring. Five beats, every house, no exceptions and no rushing the drying.
Week 0
The moisture survey
Two house-days: wall build-ups read through small openings, salts and damp mapped, sensors set, and the heating pattern of the last winter reconstructed from the bills. The retrofit is designed against what the wall is actually doing, not against a brochure average.
Weeks 1–3
The drawings & consents
Build-up drawings with vapour calculations, U-values stated honestly modest, and the conservation officer met BEFORE the application where your district needs it. Six districts keep us on their approved sheet precisely because the paperwork reads like this.
Weeks 4–8
The works
One crew, inside and out, in the order the physics wants: draught-proofing first, then floors, then walls, roofs last. Lime mortars mixed to the house’s own, boards returned grain-matched, and the site vacuumed nightly — old houses are homes first.
Month 3 & 6
The readings
Sensor reports against the model, in plain sentences. Drying curves on old masonry are gentle; the letters exist so you never wonder whether gentle is normal. (It is.)
Month 12
The second spring
Final reading, heat-demand comparison against the pre-works bills, and the sensors either stay as house instruments or come out — your choice, and either way the year of data is yours in a folder.
Fair questions
Asked at every kitchen table
The five every old-house owner arrives carrying, usually printed off a forum. The practice line below runs seven to five; Elowen answers it herself on survey days, chalk dust and all.
Why not spray foam — it’s half the price?
Spray foam is cheaper per inch and catastrophic on the wrong wall: it glues a vapour-closed layer to a fabric that dries outward, so the moisture that always moves through old masonry has nowhere to arrive. Interstitial condensation follows, then rot you cannot see, then a surveyor who declines the mortgage. We spend our weeks removing it — see our sister crew’s ledger — and we will never install it in a wall built before vapour barriers were understood.
Will it actually be warmer, or just virtuous?
Warmer, measurably: median 41 percent heat-demand reduction across 286 monitored houses, and the first thing every owner reports is the end of the radiant-cold wall — the room feels warm before the thermostat says so. But we quote U-values modestly, because an old wall’s honest promise is comfort and drying, not a passive-house certificate.
My house is listed — is any of this possible?
More of it than you fear. Cork and calcium-silicate linings are reversible by design and increasingly welcomed by officers who have seen what sealed systems do; our consent drawings carry vapour calculations and reversibility statements, and six districts now list us on their approved-craftspeople sheet. The survey tells you which of the four systems your officer has already said yes to this year.
What does the year of sensors actually cost?
Nothing extra — it is the work, not an accessory. The readings are why we can promise the dry verdict: a build-up nobody monitors is a promise nobody can check, and eleven years of letters is worth more to us than the price of a dozen loggers.
Can you do one room at a time?
Yes, and on old houses it is often the right rhythm — the survey prices each phase and the order is chosen by physics (draughts, floor, walls, roof), not by which room annoys you most. Phase two re-uses phase one’s sensors, so the whole house ends its second spring with a single coherent story in the folder.
A wall that cannot dry is a wall that is dying. Our whole trade is making an old house warm without ever forgetting which one of those two things matters more.
The conservation officer approved the cork linings in six weeks, which the street regards as a miracle. The twelve-month letter arrived with a graph I could actually read: two walls drying, one flat and healthy, and the house three degrees warmer at the same boiler setting. The folder lives with the deeds.
Two firms before them quoted spray foam over our 1890s brick and called our questions old-fashioned. Breathline read the walls for two days, showed us where the rain got in through the parapet, and fixed that BEFORE insulating. The difference in the trade is the difference between a dietician and a pusher.
They lifted our hall floor board by board and put it back with the grain matched — the join is invisible and the draught that met you at the door is simply gone. The lofts and walls came the year after, on the plan’s schedule, at the plan’s price.
Moisture surveys run year-round · works book 8 to 12 weeks out · conservation consents handled in-house · (555) 331-6058 · walls@breathlineretrofit.example
The moisture survey
Start with two days of reading the wall
The age of the house, what heats it, and anything the walls do in rain that worries you — that is enough to book the survey, and the four-system plan with honest prices follows a week later. works anywhere on the marshes and in all six districts. walls@breathlineretrofit.example