The Knowl­edge MAK­inG Ex­isT­inG HOMEs EF­Fi­ciEnT

Homebuilding & Renovating - - PORTFOLIO -

Although John and Jean knew what they wanted to achieve, their plans only re­ally came to life when they em­ployed ar­chi­tect Paul Testa, who they could work closely with and who was will­ing and able to project man­age the en­tire ren­o­va­tion.

Paul was also highly in­stru­men­tal to the en­er­gy­ef­fi­cient scheme. “From the out­set we aimed to achieve as close to the AECB build­ing stan­dard as was spa­tially and fi­nan­cially rea­son­able on the project,” he ex­plains. “It

fol­lows the broad method­ol­ogy that is used for Pas­sivhaus but has a lower per­for­mance thresh­old and a less oner­ous process for cer­ti­fi­ca­tion. We find it a very use­ful of­fice bench­mark for all the projects we do that aren’t specif­i­cally aim­ing for Pas­sivhaus.

“The ex­ist­ing bun­ga­low was cold, dark and damp. It was a pri­or­ity for Jean and John that this be­came a warm, com­fort­able and healthy home in which to re­tire,” con­tin­ues Paul. “The ex­ist­ing con­struc­tion had al­most no in­su­la­tion, de­spite the el­e­vated and ex­posed hill­side lo­ca­tion. The block and stone cav­ity walls were not suit­able for retro­fit cav­ity wall in­su­la­tion and the tim­ber floors and roof were not in­su­lated.

“The pri­or­ity was to im­prove the ther­mal per­for­mance of the build­ing fab­ric — a fab­ric-first ap­proach. This in­volved three key as­pects:

l in­su­la­tion

“We in­su­lated be­tween the sus­pended tim­ber floor joists with rigid in­su­la­tion, as well as in­su­lat­ing the ex­te­rior walls with a drylin­ing sys­tem and adding rigid in­su­la­tion be­tween and above the roof trusses. The glaz­ing through­out the build­ing is also highly ef­fi­cient as we used high-per­for­mance triple-glazed Velfac win­dows and Fakro rooflights.

l air­tight­ness

“We over­boarded the floor joists with OSB and taped the joints to prove an air­tight struc­tural deck; the walls were sealed with an in­tel­li­gent vapour con­trol mem­brane as was the roof. This was care­fully taped at all joints, pen­e­tra­tions and to the win­dow frames.

l ven­ti­la­tion

“A con­sid­ered and prop­erly de­signed ven­ti­la­tion strat­egy is key to the com­fort and health of a build­ing. In this house we utilised a me­chan­i­cal ven­ti­la­tion with heat re­cov­ery (MVHR) sys­tem. This is ducted around the build­ing sup­ply­ing fresh, pre-heated air to the bed­rooms and liv­ing spa­ces and ex­tract­ing dirty, moist air from the kitchen, bath­room and

util­ity. The heat re­cov­ery el­e­ment en­sures that min­i­mal heat is lost through ven­ti­la­tion but the oc­cu­pants are still guar­an­teed a con­sis­tent sup­ply of fresh air to give the best pos­si­ble in­ter­nal air qual­ity.

“Retro­fit work is highly chal­leng­ing be­cause houses like this are pretty fixed in their ge­om­e­try and ori­en­ta­tion. There were var­i­ous build­ing el­e­ments that in­evitably led to cold­bridges [which can al­low heat to es­cape and/or cold air to en­ter] in the con­struc­tion, and there were some mi­nor spa­tial con­straints also on in­ter­nal wall in­su­la­tion and the duct rout­ing for the MVHR sys­tem. So this also needed care­ful plan­ning and de­liv­ery on site.

“As we took a fab­ric-first ap­proach to the project we didn’t par­tic­u­larly con­sider re­new­ables such as heat pumps and biomass heat­ing as the bud­get wouldn’t stretch that far. How­ever, the house ben­e­fit­ted from a large ar­ray of ex­ist­ing so­lar pan­els on the south-fac­ing roof which were care­fully re­moved and re­fit­ted after the re-roof­ing works. These were old enough to be pay­ing the best Feed-in Tar­iff (FiTs) rate, so were well worth re­tain­ing.

The house now has com­bined gas and elec­tric bills of £800/year but with a FiTs pay­ment of £1,800/year, the cou­ple are mak­ing a hand­some an­nual profit of £1,000.”

Con­cludes John: “It was good to have some­one who was able to sug­gest pos­si­ble op­tions in­clud­ing cal­cu­lat­ing the ef­fect on ther­mal ef­fi­ciency of each po­ten­tial cut when we needed to re­duce costs. Ul­ti­mately, that was an in­valu­able part of the de­ci­sion-mak­ing process.”

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