Are floor joists like this normal?

New Build Inspections


New Member


New Member
"Engineered" joists such as those shown in your photograph are de rigeur amongst the major housebuilders now and are produced by several manufacturers. They have been successfully used for well over 10 years now. Their advantages over the original timber joist are greater strength for the depth of timber, light weight, greater achievable spans and more flexibility in positioning service runs, through their centres.

Chuck Sidfrum

New Member
Is this normal? I plan to put a weight bench upstairs...

Semi Engineered I-Joists (or I-Beam Joists), invented by Nascoe (I understand) are licensed for manufacturer to 15 plants in 6 countries.

You can find them in Australia, Canada, USA, UK. Australian standards are so much nicer written on these, for the home owners benefit.

These are typically fitted as continuous floor runs thus the whole floor should generally be considered when meeting manufacturers tolerances, thus not necessarily NHBC guidelines for each room (implied to home owners like us as seperate entities).

In the UK JJI Joists is one such company that licenses rights to manufacturer and sell I-Beam Joists. They supply Persimmon Homes, Charles Church and other builders.

Using JJI web site, you can look up your joist specification (if yours are JJI, which will be marked on them) and see the floors Serviceability Index (SI).

This is a measure of how solid (how little deflection) the floor will exhibit.

From memory, an SI index of 1.00 would give 9 or 12mm deflection across a 4m span. In our home Charles Church used the lowest spec joist (thinest, most widely spaced) across an approximate 4m span giving a theoretical SI or 1.06. I understand the joists cost less than £1,000 for our property.

For a couple of hundred pounds (according to numerous sources) they could have fitted a more substantial I-Beam floor (thicker joists, closer together), with an SI index of 7 (for example and again from memory, without checking notes), which would have meant a deflection of only a couple of mm's (3mm if I remember).

Also (in addition to fitting a higher spec instead of a lower spec) providing they had taken reasonable care in fitting the joists (leveling the fixings etc, which they did not do) then the floor would likely not have suffered from cracking and creaking noises, deflection/vibration/bounce when walking and unlevel floors.

So I would answer your question by saying that an i-joist floor system, with an index of (for arguments sake) 5 or more, which is fitted correctly would be in my opinion would be a good solid floor.

However, an i-beam floor, or SI index 1.00, fitted poorly would in my opinion be a problem just waiting to be fixed.

I can advise on using/buying £70 water level to check your floors, and how to spot the early signs of cracking/creeking sounds which would with all probability only get worse with time and not better.

I might expect a floor to be noisey after 10 or 20 years (but I don't), but I would definately not expect it to be noisey in the first week, and getting progressively worse for the next 1-2 years.

Every Charles Church and Persimmon Home I have personally walked round has shown a noisy creaking/cracking floor issue. This can be heard from underneath (usually caused by the ceiling/plasterboard, and for which british gypsum suggest strengthening the floors) when someone (or a dog will do) walks above you.

You will first notice this in the most trafficed rooms, e.g. bedroom 1. But eventually it is likely all rooms will exhibit the problem (even bedroom 5 if just used as a box room), and that the whole floor system would need remedial works to check the joists (design, plan, installation, fixings etc) and strengthen.

I would personally not advise cross bracing (herringbone noggins) as a solution to strengthen. Preferring the better supported joist plating and solid blocking. ALternatively I would consider the IBS2000 engineered blocking solution which seems succesfull.

Canada (where Nascor is based) Building Control has been involved in testing solutions to this problem (where perhaps the joist design is over spanned) and made the above recommendations in support of plating and solid blocking or the approved IBS 2000 approach. You tube has a wonderful demo of cross bracing versus IBS2000 system to add support to an I-Beam joist system. Albeit the solid blocking example shown (is perhaps unfairly) not fixed to the joists in a way I would recommend, because the joint with the joist is critical in solid blocking working to it's best.

The IBS 2000 merely combines the economics of cross bracing, with the benefits of solid blocking with a good fixing method.

If my wording has confused, apologies, and I will try to explain any point further.

Privately I can provide further information to help with this problem with UK builders and NHBC - but you didn't hear that further information from me ;-)

Whilst the NHBC talks of 9mm (or is it 12mm) deflection in a floor as normal, it's unclear wehther they refer to the finished floor as a whole system, or just an individual joist bearing a specific weight. The builder is always happy to test this figure (often with furniture in situ, and floor already deflected, before they add a body as weight), as they always seem to pass this test . . . maybe red bull f1 cars have similar thoughts on the older front wing loading tests :)

But, much more importantly is the advice I received claiming that with regards to floor bounce (vibration, deflection) for a 4m a deflection of more than 1.2mm would likely be unsatisfacotory for a person walking to feel comfortable with the floor. A figure that I beleive many new homes with 4m span i-beam joist of the lowest spec (SI 1.0), would fail.

My concern is when one comes to sell the property. What was hard to notice when one originally purchased the property, might become very obvious 5 years down the line. And I wonder if reported outside the 2 year warranty whether NHBC would take responsibility (it's hard enough to get them to take responsibility when it is reported in the first 2 years). Are own current for cost of repairs to our home, including alternative accomodation is over £40k.
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