Getting builders out of a flooring fix

Some of the blunter sections of the construction industry have renamed the amended Part L of the Building Regulations Part Hell. While the changes are intended to improve building performance, they've also caused a fair few headaches for builders and architects who, to comply, have had to adapt the way they work and the construction products they use.

One real hangover could have been caused by the impact of revisions to Part L (and Parts J and F) on the use of timber joists and I-beams in conjunction with masonry walls. But that was until Glenrothes-based Cullen Building Products came up with a cunningly designed solution.

Managing director Doug Cullen explained: "Under the revisions to Parts L/J/F covering thermal performance and air leakage in buildings, timber and timber engineering joists can no longer be built into the masonry inner leaf. The seepage of air and heat from buildings occurs because approximately 80% of floor joists were being built into walls. The joists and the mortar in the walls are prone to shrinking and that leads to air seepage and heat loss."

The implications of this development were clearly serious. If the use of timber and engineered wood joists in masonry buildings was restricted, alternatives would have to be found, and that might mean an increase in the use of concrete. That in turn would have a knock-on for the building process, notably delaying and complicating the installation of the flooring itself, whether that's a wood-based sheet material substrate, like chipboard or OSB, or, of course, a timber floor.

But while the problem looked thorny, Cullen was undeterred. The company, which has been one of the lead suppliers of connector products to the engineered timber sector since1977 and prides itself on its "can do approach" set about developing a connector solution which enabled compliance with the new rules and "safeguarded the market for timber joists in masonry construction".

"There's no point in putting your head in the sand," said Mr Cullen. "If there's a problem out there in the timber engineering industry and we as connector manufacturers can help, we see that challenge as our business. "

The company worked on the project to crack the dual problem of air seepage and safe loading with their consulting engineers, Timbersolve. The end product is described as an "innovative joist to masonry connection" called the JHR.
When used in conjunction with parallel straps (PS), Doug Cullen claims that his company's new connector will "enable the construction industry to quickly meet the challenges posed by Part L".

"The JHR can be connected quickly and easily, without subsequent safety problems being created on site, and could therefore increase the speed of the build process."

Developing the JHR, Cullen also took on board the need to design a safe and efficient method of supporting floors actually during construction.
"Conventionally joist hangers have been accredited by testing them built into fully cured masonry walls, with a minimum of three courses of masonry above as stipulated in BS6178," he said. "But the resulting safe-working loads for the hanger were not intended for use during the construction phase as neither the appropriate 28-day cure period is allowed for, nor is sufficient masonry constructed above before floors are installed. As a result, when newly laid floors have been used as working platforms, there have been cases of floor collapse and injury."

Cullen has qualified the limits of the JHR with a new type of test defining the working load for the hanger during construction, so workers can limit the live load to safe levels. The company has also produced an illustrated, easy-to-follow guide on safe fixing of floor decking and construction of party walls off newly laid floors.

Having met the challenges of Part L, Cullen's attention has now turned to producing a backer-free I-beam hanger. This soon-to-be-launched product will transfer loads between I-joists at 90 degrees without the need for the traditionally used costly and time-consuming backer blocks and web stiffeners.
Commenting on this latest innovation, Dr Luke Whale, a leading consultant to the Engineered Floor industry said:

"The largest single problem we encounter on site is caused by either absent or improperly fitted backer blocks. Removing the need for these is probably the most significant hanger innovation our industry has seen."