Two steel beams (one on each leaf) versus One single beam

[JonHeath]

Hi all,

I'm currently in conversation with my structural engineer about design and calcs required for creating a 5m gap in the back of my house into a new extension.

He has come up with two options:

Option 1. This will see two steels. One for the inner leaf and one for the outer leaf. The advantage of this, is that the inner leaf one (which takes more weight) can run further down the blockwork/pads, whilst the outer one will need less overlap with the blockwork/pads. Overall gain is that I don't need a masonry pier that sticks out on the left hand side. Hopefully my sketch below will make what I'm trying to say a lot clearer.

Untitled

• JonHeath
• 7 Feb 2015
• 1

Option 2 is having just a single steel sitting across both leafs (more standard I believe?). The downside of this is that it would require a masonry pillar at the left hand side so that there is enough surface to take the weight. Without a masonry pillar the steel would need to sit on that much of the wall that it would be exposed to the outside.

I've not done this before so I'm interested to hear more experienced views on both options. Option 1 obviously sounds better to me, but are there costs or concerns that I've not thought of?

Many thanks
Jon

 

[jeds]

I'd always go for two beams for a cavity wall anyway. A single beam that span would only be a 203mm width so you'd need to plate it to cover the width of the wall. A single beam that span is also a beast to handle. Go with two beams. much easier and less messing about with piers.

 

[cjard]

2 beams can also be insulated in the middle. They may be specced to be bolted together so will largely act as one anyway, but as jeds says are easier to handle and set. It's handy to have them at different heights - you might even want the inner one to sit higher than the outer so you can insulate its underside. The outer one, possibly both might need alvanising too. I have this arrangement on my current building (and the steel to go that span weighs about 500kg !) and it worked well. Glad I had a JCB to lift em in though

Ring round for quotes - I had responses ranging from 700 to 1800 per lintel, and mine were specced as: 203x133x25 inner, 305x165x54 outer, galvanised, with extra plate welded top and bottom

Local steelworks company that usually put up massive agri buildings did them in the end, and by waiting until they had a big job going for galv I got a discount..

 

[noseall]

Two beams every time.

 

[JonHeath]

Thanks for the replies guys, that's helped me make my mind up.

cjard - those quotes, were they just for the steel or installing the steel too?

They just seemed higher than I was expecting if it was just the steel. For example at http://www.parkersteel.co.uk a 6.1m length of 203x133x25 shotblasted and painted red is £255. A 6.1m length of 305x165x54 shotblasted and painted red is £389. I've no affiliation to that site, it's just the first one I came across when googling.

 

[noseall]

. For example at http://www.parkersteel.co.uk a 6.1m length of 203x133x25 shotblasted and painted red is £255. A 6.1m length of 305x165x54 shotblasted and painted red is £389. I've no affiliation to that site, it's just the first one I came across when googling.

Does this include hole drilling and spacers etc?

 

[JonHeath]

. For example at http://www.parkersteel.co.uk a 6.1m length of 203x133x25 shotblasted and painted red is £255. A 6.1m length of 305x165x54 shotblasted and painted red is £389. I've no affiliation to that site, it's just the first one I came across when googling.

Does this include hole drilling and spacers etc?

No it won't do. Would that make the price go into the £1400+ bracket (£700+ per beam) spoken about above)? I wouldn't have thought so?

If so then I go back to my original question. Is two beams therefore worth it?

 

[cjard]

Thanks for the replies guys, that's helped me make my mind up.

cjard - those quotes, were they just for the steel or installing the steel too?

That was the price of a 4600mm 305x46kgm with an extra 10 inch plate fully welded all the way along the bottom flange and spacers welded on over 10 holes in the web at about 400 centres, plus a 4600mm 203x25kgm with an extra 8" plate welded on the centre 600mm of the top flange, 10 holes, 10 bolts/nuts to fix the two together and then the whole thing hot dip galvanised. This whole thing, fully fabricated, prepped and delivered to site was £700.

Steel only was about half that price and I could possibly have bought a welder, done the fab myself and sent them for galv too for about the same money but I don't have the time, or the size of trailer needed to get a lintel that size to and from the galvanisers! :/

The galv was the thing that pushed it up for most places.. A few of my steel fab quotes were similar for the actual steel, it was only when the galv was added on that the price jumped

Installation was done by yours truly, a couple of loading straps and the back actor of my aging 3cx - it wasn't as easy as it sounds because the wall already existed, so it needed needling and acrowing in 3 places, block upstands were required to meet the acrows on the outside due to low levels of solid ground. The steels had to be rested at the base of the wall before the acrows were placed and we actually only knocked out enough of a wall strip to just fit the steel in, rather than knocking the whole opening. We did this so we could load the top of the steel with a stiff mix of mortar and use scissor jacks on top of the old wall to lift the steel into place for a good packing up against the existing wall, then cast concrete padstones under either end for support. Had the wall been being built anew it would have taken a fraction of the time. As it was it took about a man-week of time

 

[freddiemercurystwin]

A 203 will not do a 20ft opening.

 

[JonHeath]

Thanks for the replies guys, that's helped me make my mind up.

cjard - those quotes, were they just for the steel or installing the steel too?

That was the price of a 4600mm 305x46kgm with an extra 10 inch plate fully welded all the way along the bottom flange and spacers welded on over 10 holes in the web at about 400 centres, plus a 4600mm 203x25kgm with an extra 8" plate welded on the centre 600mm of the top flange, 10 holes, 10 bolts/nuts to fix the two together and then the whole thing hot dip galvanised. This whole thing, fully fabricated, prepped and delivered to site was £700.

Steel only was about half that price and I could possibly have bought a welder, done the fab myself and sent them for galv too for about the same money but I don't have the time, or the size of trailer needed to get a lintel that size to and from the galvanisers! :/

The galv was the thing that pushed it up for most places.. A few of my steel fab quotes were similar for the actual steel, it was only when the galv was added on that the price jumped

Installation was done by yours truly, a couple of loading straps and the back actor of my aging 3cx - it wasn't as easy as it sounds because the wall already existed, so it needed needling and acrowing in 3 places, block upstands were required to meet the acrows on the outside due to low levels of solid ground. The steels had to be rested at the base of the wall before the acrows were placed and we actually only knocked out enough of a wall strip to just fit the steel in, rather than knocking the whole opening. We did this so we could load the top of the steel with a stiff mix of mortar and use scissor jacks on top of the old wall to lift the steel into place for a good packing up against the existing wall, then cast concrete padstones under either end for support. Had the wall been being built anew it would have taken a fraction of the time. As it was it took about a man-week of time

Thanks for the extra info. You originally said 700-1800 per lintel so I was imaging at least 700 * 2, but 700 all in seems very reasonable especially with all the mods described. Do you know why they specified it be galvanised?

 

[cjard]

A 203 will not do a 20ft opening.

I think the SE that specified a 203x203x113 UC for a 22ft span in my house might disagree, but I've since had the span broken up so the steel can become a 25kgm one; didn't fancy lifting 900 kilos of steel to the third floor

Still got a few 18ft 203x203x46 on the first floor though, not that it violates your rule..

 

[cjard]

Thanks for the extra info. You originally said 700-1800 per lintel so I was imaging at least 700 * 2, but 700 all in seems very reasonable especially with all the mods described. Do you know why they specified it be galvanised?

My quotes varied from 700 - 1800 per lintel (2 steel beams constructed as advised form 1 lintel), and I needed two lintels. After plumping for the £700 lintel I have spent £1400 on lintels (=4 beams and a lot of welding)

Galv because they're in the corrosive environment of an external wall, brick, stone, lime mortar and even cement render for its sins.
I wanted to just let the work experience kid loose with a bit of hammerite, but given that the galv quote per lintel (from the place I went to in the end) was £100 I reasoned that I'd get a better value job done in galv - they couldn't be painted fast enough or well enough to beat

Odd thing; the galv was occasionally the lions share of the quote and it's usually done by weight so it shouldn't really have varied between quotes. I can only assume, because I went to a guy who makes massive steel framed buildings for farms and I was prepared to wait until he had tens/hundreds of tons going for galv, that he was probably able to add my galv on and secure a better rate for it in the face of the bigger order