Green Building Forum - Eco - metal web joists: deflection Sat, 08 Aug 2026 17:05:47 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218819#Comment_218819 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218819#Comment_218819 Sat, 07 Feb 2015 16:42:32 +0000 ward32
Max span of longest joist = 5.2m

I intend to glue 22mm T&G boards to the joists.]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218820#Comment_218820 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218820#Comment_218820 Sat, 07 Feb 2015 16:54:21 +0000 ringi Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218821#Comment_218821 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218821#Comment_218821 Sat, 07 Feb 2015 16:55:25 +0000 PeterStarck Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218822#Comment_218822 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218822#Comment_218822 Sat, 07 Feb 2015 17:09:05 +0000 ward32 Dead load = 0.45kN/m2
Imposed load = 1.5kN/m2
Bottom chord dead load = 0.2kN/m2

I'm mostly concerned with deflection when walked on, maybe worried about nothing!

Should I just go with 600mm joist spacing?]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218824#Comment_218824 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218824#Comment_218824 Sat, 07 Feb 2015 18:04:07 +0000 cjard
Put another way, if you nip down to the local rugby club and ask 20 players (100kg) and their wives (50kg) and ask them to stand paired up, one couple per square metre of your fully built, carpeted, insulated, decked etc floor.. Then your floor in the middle would have sagged by about the thickness of your index finger]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218899#Comment_218899 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=218899#Comment_218899 Sun, 08 Feb 2015 16:16:28 +0000 ward32 Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219018#Comment_219018 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219018#Comment_219018 Mon, 09 Feb 2015 21:16:27 +0000 DarylP That is an awful lot... it will feel like a spring....:shocked:
400mm c/cs, and maybe deepen the section, or widen the flanges?

Good luck...:smile:]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219022#Comment_219022 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219022#Comment_219022 Mon, 09 Feb 2015 22:05:51 +0000 atomicbisf
If there are any walls or fixtures upstairs around mid span that amount of deflection will cause a lot of cosmetic damage surely.

Ed]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219026#Comment_219026 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219026#Comment_219026 Mon, 09 Feb 2015 22:36:05 +0000 ringi
Also some of this deflection will happen as soon the the floor and ceiling is installed, before you build any walls on top of the floor.]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219068#Comment_219068 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219068#Comment_219068 Tue, 10 Feb 2015 14:36:06 +0000 fostertom Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219093#Comment_219093 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219093#Comment_219093 Tue, 10 Feb 2015 17:22:16 +0000 djh Posted By: ward32reducing the spacing from 600mm to 400mm
We have metal web joists and I'm very pleased we chose them. One of the main reasons for using metal web joists is the ease of running services. But there is a downside. Unlike either traditional joists or I-beam joists, you can't cut through the metal web joists - neither the webs nor the flanges. So you have to run services where the openings are. That can be a bit tricky for big stuff like ventilation ducts and soil pipes, especially near the MVHR unit where there are lots of ducts. We've ended up with a soil pipe run across the floor of the plant room because the space between the joists is so full of ventilation ducts. I suspect that reducing the joist spacing from 600 mm to 400 mm would magnify this problem, so I'd be nervous about doing it. I'd certainly suggest getting full layout plans for all pipework coordinated with the joist plans before ordering to make sure it is possible to lay your services.]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219104#Comment_219104 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219104#Comment_219104 Tue, 10 Feb 2015 18:14:36 +0000 Simon Still Posted By: djh
Posted By: ward32reducing the spacing from 600mm to 400mm

Unlike ....I-beam joists, you can't cut through the metal web joists - neither the webs nor the flanges.

You can only cut the web on I-beams and larger than a certain size/within a certain distance of the end, the holes then need reinforcement with (expensive) metal plates. 75mm vent ducts require this in most places in my build - and cutting the holes and fitting the plates took me a few days. I'd definitely go for metal web next time (though I'm sure they have their own idiosyncrasies)]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219121#Comment_219121 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219121#Comment_219121 Tue, 10 Feb 2015 20:23:17 +0000 Cerisy
It was also important to allow for boxing in for drainage behind the toilets, giving more flexibility, and having our airing cupboard between the two bathrooms so we can use part of it for drain runs and manifolds.

Yes, it would have been good to have the services layouts done before the frame design was agreed, but even for a retired architect it was a step beyond my expertise!!]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219205#Comment_219205 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219205#Comment_219205 Wed, 11 Feb 2015 16:29:48 +0000 CWatters Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219220#Comment_219220 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219220#Comment_219220 Wed, 11 Feb 2015 18:30:15 +0000 PaulJ Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219236#Comment_219236 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219236#Comment_219236 Wed, 11 Feb 2015 20:12:55 +0000 Paul in Montreal
See http://www.johnbridge.com/vbulletin/deflecto.pl

2x12" at 16" spacing will give you the same deflection as your metal web joists.

Paul in Montreal.]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219241#Comment_219241 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219241#Comment_219241 Wed, 11 Feb 2015 20:47:04 +0000 Timber
Engineered timber joists stand more of a chance of being 'bouncy' than solid timber joists. It is not really a function of deflection as such, more a function of springyness!

You might be perfectly fine, and a deflection limit of 14mm is totally normal and what is stated in the design codes etc, but sometimes you get unlucky and the floor ends up being springy.]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219455#Comment_219455 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219455#Comment_219455 Fri, 13 Feb 2015 15:48:27 +0000 djh Posted By: CerisyI'm slowly fitting all the services into our metal web joists. Yes, they limit in some areas (the shower tray outlet has to be exactly right against the joists underneath!),
Yes, we had one shower that we had to move about 100 mm and build a double stud wall in consequence.

Yes, it would have been good to have the services layouts done before the frame design was agreed, but even for a retired architect it was a step beyond my expertise!!

Indeed. My architect was telling me that in a new project where the internal walls are masonry and loadbearing, the question is giving him some reasons to scratch his head a bit.

Posted By: PaulJwhen the design needs strongbacks (a timber section) running at right angles to the joists, or they are supported in places with engineered or solid timber joists.

Yes, we have a central beam and intermediate strongbacks that complicate things, although the strongbacks also provide useful support for wires and the smaller pipes.

We've been discovering this past week how interesting it is to push insulation up into the ceiling!]]> Eco - metal web joists: deflection https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219468#Comment_219468 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13076&Focus=219468#Comment_219468 Fri, 13 Feb 2015 16:52:43 +0000 Cerisy
Stuffing the 75mm glass fibre in two layers wasn't too bad, it's the 140mm that I dread!! But, it's good to get some of a nasty job out of the way!! Back to wiring ....]]>