Choos­ing a build sys­tem

No con­struc­tion method scores a per­fect 10 on all fronts, but for ev­ery scheme there’s an op­ti­mum way to build, de­pend­ing on your pri­or­i­ties. Emily Brooks takes a look at how the de­ci­sion gets made in the real world

Build It - - CONTENTS -

With a wide ar­ray of struc­tural meth­ods on the mar­ket, here’s our guide to find­ing the right op­tion for your project

Abroad range of fac­tors goes into work­ing out the best struc­tural sys­tem for your project. The bal­ance could be tipped by a com­bi­na­tion of con­sid­er­a­tions, or it might be a sin­gle in­flu­ence that tilts the scales in favour of a par­tic­u­lar tech­nique.

Pro­fes­sional project man­ager Char­lie Laing’s last few builds for clients of­fer an ex­cel­lent in­sight into the think­ing that goes into choos­ing a con­struc­tion sys­tem. For a house in Croy­don, the own­ers went for tim­ber frame that of­fered them the right com­bi­na­tion in terms of bud­get, aes­thet­ics and per­for­mance (bet­ter than Build­ing Regs stan­dards).

A scheme in Buck­ing­hamshire was con­structed with in­su­lat­ing con­crete form­work (ICF) to help achieve some de­mand­ing air­tight­ness tar­gets; whereas the ar­chi­tects for an Ox­ford­shire house spec­i­fied steel frame to en­sure the highly de­tailed be­spoke de­sign would be fully re­alised.

For an­other self-build in Lon­don, mean­while, ma­sonry proved to be the best fit: “The house may get rented out at some point, and the clients have a per­cep­tion that brick and block will be a ro­bust so­lu­tion for this pur­pose,” says Char­lie, who is op­er­a­tions di­rec­tor at CLPM.

So, what do you need to know when de­cid­ing which sys­tem will best suit your goals for a new home? And how can you come to the right con­clu­sion?

The main sys­tems

Be­fore we get into the nuts and bolts, it’s worth a quick run through of the key op­tions. Build­ing in con­ven­tional ma­sonry (brick and block) is still the stan­dard choice for many new homes. With this fa­mil­iar route, cav­ity walls are con­structed by hand and filled with in­su­la­tion on site.

Next up is tim­ber frame; pop­u­lar across the UK, but espe­cially preva­lent in Scot­land, it comes in a few guises. With stick builds, the frame is all as­sem­bled on site, but this is an ap­proach that’s be­com­ing less com­mon­place as pre­man­u­fac­tured meth­ods take prece­dence. You can go for open-panel sys­tems, which see a fac­tory-made frame de­liv­ered to site with the in­ner studwork left open (so the in­su­la­tion, plumb­ing, electrics etc are in­stalled in situ). Or opt for closed-panel, where even more of the work is done off-site, with in­su­la­tion pre-fit­ted and open­ings for fen­es­tra­tion al­ready cut. In some cases, win­dows, doors and ex­ter­nal cladding may even be in place.

Struc­tural in­su­lated pan­els (SIPS) are an­other fac­to­ry­made sys­tem. These wall and roof el­e­ments con­sist of a layer of in­su­la­tion sand­wiched be­tween two sheets of tim­ber. If you pre­fer a more solid feel, in­su­lat­ing con­crete form­work (ICF) is made from hol­low blocks of poly­styrene, re­in­forced with steel re­bar and pumped full of con­crete.

Some­times more than one sys­tem is used. For ex­am­ple, ICF might be spec­i­fied for a base­ment, with an­other

tech­nique from the ground up. Mean­while, oak frame homes – which are pop­u­lar for their in­nate char­ac­ter – are typ­i­cally wrapped in SIPS or sim­i­lar in­su­lat­ing pan­els in or­der to achieve the de­sired en­ergy per­for­mance and air­tight­ness. And most ma­sonry and tim­ber builds will in­clude some steel­work to sup­port dra­matic de­sign fea­tures such as wide spans of glazed doors.

The tip­ping points

With the ex­cep­tion of green oak frame, a house’s fi­nal ap­pear­ance has lit­tle to do with the un­der­ly­ing struc­ture. Tim­ber pan­els can be clad in brick slips, for in­stance, while block­work walls can be hung with tim­ber cladding. Self­builders there­fore tend to be guided by three big fac­tors: cost; how long the project will take; and en­ergy ef­fi­ciency.

“You could build any de­sign you can think of with any form of con­struc­tion. What peo­ple want is for it to be cost­ef­fec­tive,” says ar­chi­tec­tural tech­ni­cian Granville Fal­shaw of Fal­shaw Homes. That idea is backed up by the Build It Es­ti­mat­ing Ser­vice guide on page 83, which shows that walling sys­tems for ma­sonry and tim­ber frame come in at very sim­i­lar price points. Us­ing SIPS or ICF will add to your con­struc­tion costs, but these sys­tems can of­fer ben­e­fits in other ar­eas. Green oak is of­ten at the top-end in terms of up­front prices, but the pre­mium you pay will usu­ally be re­flected in the end value of the house.

Char­lie Laing points out that it’s tough for novice self­builders to get to grips with as­sess­ing the cost of dif­fer­ent sys­tems. “It’s pos­si­ble to go shop­ping for tim­ber frames – which is some­thing you’ll strug­gle to do with ma­sonry – but you do need to be clear about who’s in charge of the de­sign and who’s in­voic­ing for which el­e­ments. You don’t

want to end up pay­ing for the same thing twice,” he says. “Frame prices can also be dif­fi­cult to com­pare: do all the quotes al­low for the same things?”

As for get­ting quick build times, it’s not all about what hap­pens once the ma­te­ri­als are de­liv­ered. “Tim­ber frame, SIPS and ICF are cham­pi­oned for their speed. If by this they mean speed on site, then that’s true,” says Char­lie. “But if you in­clude time spent on the de­sign, then things start to even out.” If you’re us­ing a pre­fab sys­tem, once the plans have been agreed, you’ll also need to fac­tor in a lead time for pro­duc­tion, which typ­i­cally takes any­where from 8-12 weeks for sys­tems such as tim­ber frame and SIPS.

When it comes to en­ergy ef­fi­ciency, it’s pos­si­ble to achieve high stan­dards with any sys­tem. As a rule, how­ever, the more off-site fab­ri­ca­tion there is, the more straight­for­ward it will be to achieve the build qual­ity and per­for­mance you wanted. This ex­tra de­gree of cer­tainty is, for many, a de­cid­ing fac­tor. “Time in the fac­tory is much more ef­fi­cient as you don’t have to con­tend with the weather, or con­straints with the site or equip­ment,” Jonathan Tip­per from Gre­gory Phillips Ar­chi­tects says of us­ing SIPS con­struc­tion: “Imag­ine build­ing a win­dow on site rather than in a fac­tory – there’s no com­par­i­son. The lat­ter route al­lows a greater de­gree of qual­ity con­trol.”

De­sign fac­tors

Although it’s com­mon for houses to be de­signed with­out the ar­chi­tect know­ing how they’ll be built, some fea­tures might sug­gest the use of one sys­tem over an­other. SIPS can bridge fur­ther than tim­ber frame, for ex­am­ple, but dra­mat­i­cally large spans can only be achieved with steel. If you want some curves, ma­sonry is ideal and ICF can cope with a few, but fac­tory-pro­duced sys­tems may not suit.

An­other con­sid­er­a­tion is that de­sign­ers ex­pe­ri­enced in us­ing par­tic­u­lar sys­tems may be bet­ter placed to get the best re­sults for your project in terms of build­abil­ity and af­ford­abil­ity. Oak frame is a case in point, as it’s im­por­tant to plan the liv­ing spa­ces to suit the span ca­pa­bil­i­ties of the struc­tural posts and beams. Sim­i­larly, with pre­fab meth­ods, if you can work to stan­dard sizes as much as pos­si­ble, you’re more likely to keep costs down.

In terms of flex­i­bil­ity of in­ter­nal lay­outs, build­ing with ma­sonry means you can hang pretty much any­thing off the walls and, should you wish, spec­ify beam and block floors (see page 111 for the ben­e­fits of this floor­ing sys­tem). Mean­while, most tim­ber frame meth­ods al­low you to eas­ily choose be­tween open plans and par­ti­tioned in­te­ri­ors – but the walls aren’t as solid for fix­ing. Try up­grad­ing to lin­ings you can screw di­rectly into, such as Fer­ma­cell or Bri­tish Gyp­sum’s Gyproc Habito plas­ter­board.

If you want flex­i­bil­ity about how the de­sign plays out on site, pre­fab­ri­cated sys­tems may not be for you. “You don’t want to be cut­ting into struc­tural pan­els, as even small holes will im­pact on ther­mal per­for­mance,” says Char­lie. On the other hand, ma­sonry struc­tures are pretty adapt­able. “You can bash holes in them with­out too much con­cern,” he says.

The po­ten­tial for fu­ture changes may also be a fac­tor for you. Gen­er­ally, tim­ber sys­tems and ICF are harder to al­ter than brick and block builds (and in all cases you’ll need to seek ad­vice from a struc­tural en­gi­neer). You can, how­ever, look to in­sert lin­tels and even capped-off ser­vices at points where you might want to ex­tend fur­ther down the line. It will cost a lit­tle more now, but pro­vide greater flex­i­bil­ity for you and any fu­ture own­ers.

Who makes the de­ci­sion?

Ul­ti­mately, the joy of self-build­ing is that you get to choose ev­ery­thing that goes into your new home – but many peo­ple are happy to be guided by their de­signer. Jonathan

says it’s quite rare for clients to have al­ready made up their minds; although some­times they come with the looser idea that they want their project to be eco-friendly, which may nudge the ar­chi­tect in a par­tic­u­lar di­rec­tion. “We gen­er­ally take the lead on con­struc­tion method and ad­vise on the most prac­ti­cal op­tion de­pend­ing on the site, the size of the house and the longevity re­quired,” he says.

With all of the re­cent projects CLPM has worked on, ei­ther the self-builder or their ar­chi­tect al­ready had their struc­tural choices in mind. “They were look­ing for us to dou­ble-check their logic and the deals they’d struck with their sup­pli­ers,” says Char­lie.

If you’re tak­ing on the role of project man­ager your­self, this may sway you to­wards one build sys­tem or an­other. The more pre­fab­ri­cated the method, the less on site labour and ma­te­ri­als there are to man­age, which can make things sim­pler. But you may feel more com­fort­able with the slowand-steady pace of ma­sonry, and how the var­i­ous trades’ works are stag­gered. And if there’s more to do on site, there are more op­por­tu­ni­ties to pitch in and learn prac­ti­cal skills, which is a big draw if you want to be hands-on.

Fi­nance & war­ranties

If you need a mort­gage for your self-build, the lender will usu­ally re­quire you to se­cure a 10-year struc­tural war­ranty. You’ll need to en­sure your war­ranty provider has ap­proved the prod­ucts and sys­tems you in­tend to use (most have a list on­line that you can search through or down­load).

With spe­cial­ist self-build mort­gages, the money is re­leased in stages – ex­actly how this is done will shape your cash flow pro­file, which may suit dif­fer­ent struc­tural sys­tems over oth­ers. Ar­rears prod­ucts re­lease funds af­ter the project has reached a cer­tain stage (foun­da­tions, wall plate, etc). This may not be ideal if you’re work­ing with tim­ber frame (un­less you have a healthy cash re­serve), as with this method a large per­cent­age of the bud­get gets paid out up front for the be­spoke house shell. An ad­vance stage payment mort­gage, where the funds are re­leased prior to each phase of work com­menc­ing, may be a bet­ter so­lu­tion for you – but it will nar­row your choice of lenders.

Spe­cial­ist self-build lend­ing has come on greatly in terms of the avail­abil­ity of fi­nance for a breadth of dif­fer­ent struc­tural sys­tems. Things can be a lit­tle dif­fer­ent in the broader mort­gage mar­ket, how­ever. The con­ser­va­tive fi­nan­cial in­dus­try tends to con­sider any­thing out­side of con­ven­tional ma­sonry walls with a slate/tile roof to be ‘non-stan­dard con­struc­tion’. This means, if you de­cide to sell, prospec­tive buy­ers may have to search harder for a mort­gage. This is where that 10-year war­ranty you ar­ranged comes into play: with this in place, things will be much eas­ier for any fu­ture pur­chaser. If you’re build­ing with a view to sell­ing up and mak­ing a profit, check out Tim Do­herty’s guide to what you need to con­sider on page 94.

In­de­pen­dent re­search com­mis­sioned by the Mod­ern Ma­sonry Al­liance shows that 76% of home­own­ers never asked what the build­ing was made from when buy­ing their home. This sug­gests the pros and cons of dif­fer­ent struc­tural sys­tems aren’t on most peo­ple’s radar; but for self-builders look­ing to cre­ate some­thing tai­lored to their needs, the choice can be cru­cial to a suc­cess­ful project.

SIPS pan­els on the move in the fac­tory of Scot­tish de­sign and build com­pany Makar. The more off-site con­struc­tion goes into your project, the more straight­for­ward it will be to get the air­tight­ness and ther­mal ef­fi­ciency you set out to achieve

A brick-and-block house by Fal­shaw Homes. Ma­sonry sys­tems are still con­sid­ered the norm and most prop­er­ties are built this way in the UK

Left: The highly be­spoke na­ture of this Hamp­shire project by AR De­sign Stu­dio re­quired the use of a steel frame build sys­tem

We­ber­haus uses a breath­able closed-panel tim­ber frame sys­tem to cre­ate healthy, ef­fi­cient homes – in­clud­ing this stun­ning con­tem­po­rary de­sign

In­su­lated con­crete form­work (ICF) con­sists of locked-to­gether poly­styrene blocks, which are re­in­forced with steel re­bar and then filled with con­crete; this is a Nudura sys­tem, shown mid-pour. The tech­nique can de­liver strong air­tight­ness and in­su­la­tion, and is quicker and more weather-re­sis­tant than block­work con­struc­tion

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.