Why are roofs on new builds made out of wood and not steel?

v638sg7k1a92bx · 01-06-2020 12:18AM #1

Is it purely down to cost? Seems that steel is so much more sturdy than wood and that roofs are prone to problems why are roofs on new builds not made out of steel?
New houses being built on our road and the roof is al made out of timber.

cnocbui · 01-06-2020 03:03AM

Cost: both the material and the labour required to work with it.

Mellor · 01-06-2020 03:23AM

Anaya Sticky Self-portrait wrote: »

Is it purely down to cost? Seems that steel is so much more sturdy than wood and that roofs are prone to problems why are roofs on new builds not made out of steel?
New houses being built on our road and the roof is al made out of timber.

Steel is no more sturdy than wood. The strength of each is down to the size of the member. Steel roofs are prone to same problems.

Attics are generally not floored, which suits timber joints more than steel.

v638sg7k1a92bx · 01-06-2020 09:35AM

Mellor wrote: »

Steel is no more sturdy than wood. The strength of each is down to the size of the member. Steel roofs are prone to same problems.

Attics are generally not floored, which suits timber joints more than steel.

So why are sky scrapers not made out of timber?

Can steel get woodworm and dry rot?

Will the trusses in an steel roof bow like a timber one?

Lumen · 01-06-2020 10:24AM

Wood is a reasonable insulator, whereas steel is terrible, so it is more difficult to avoid cold bridges and interstitial condensation, which is as bad for steel as it is for wood.

I think you're on to something with the skyscrapers. You should patent timber reinforced concrete before someone else does.

dathi · 01-06-2020 11:22AM

Lumen wrote: »

Wood is a reasonable insulator, whereas steel is terrible, so it is more difficult to avoid cold bridges and interstitial condensation, which is as bad for steel as it is for wood.

I think you're on to something with the skyscrapers. You should patent timber reinforced concrete before someone else does.

https://www.treehugger.com/green-architecture/worlds-tallest-timber-tower-topped.html
to late for that

Mellor · 01-06-2020 11:53AM

Anaya Sticky Self-portrait wrote: »

So why are sky scrapers not made out of timber?

Can steel get woodworm and dry rot?

Will the trusses in an steel roof bow like a timber one?

Because the size of timbers are limit by the size of trees. They are also less space efficient for a given strength. Neither of those factors are relevant in domestic construction. I'd have thought that was fairly obvious.

No steel doesn't rot or get worm. Both of which are preventable.
On the other hand timber doesn't corrode or rust, steel does. Also preventable.

Lightweight Steel trusses move more than timber actually.
Steel is much more susceptible to movement due to temperature changes. This movement is a significant concern in steel roofs.

listermint · 01-06-2020 04:12PM

I don't know of any problems with wood in roofs on new houses ??

The ones in mine are over 40 years old.

jack of all · 01-06-2020 09:51PM

All well answered above, but steel and condensation is a corrosion risk. Light steel sections can fail spectacularly in (even a small) fire situation.

01-06-2020 10:16PM

listermint wrote: »

I don't know of any problems with wood in roofs on new houses ??

The ones in mine are over 40 years old.

I nearly bought a 200 year old house once and the timber roof was the only thing not wrote off!
Beautiful craftsmanship too.

v638sg7k1a92bx · 01-06-2020 10:40PM

Mellor wrote: »

Because the size of timbers are limit by the size of trees. They are also less space efficient for a given strength. Neither of those factors are relevant in domestic construction. I'd have thought that was fairly obvious.

No steel doesn't rot or get worm. Both of which are preventable.
On the other hand timber doesn't corrode or rust, steel does. Also preventable.

Lightweight Steel trusses move more than timber actually.
Steel is much more susceptible to movement due to temperature changes. This movement is a significant concern in steel roofs.

Can we please stop with these type of nonsense answers. Are we in artic circle or Sahara desert?

Markcheese · 01-06-2020 11:51PM

Anaya Sticky Self-portrait wrote: »

Can we please stop with these type of nonsense answers. Are we in artic circle or Sahara desert?

Have you ever been in an attic on a sunny day ? It'd cook you ,!!! ,mind you ,doesn't cause much problem in northern Australia,where it tends to be about termites ( Our winter temp are pretty mellow all right )
I dare say if you want a steel roof you could have one ,

muffler · 02-06-2020 12:11AM

Anaya Sticky Self-portrait wrote: »

So why are sky scrapers not made out of timber?

Can steel get woodworm and dry rot?

Will the trusses in an steel roof bow like a timber one?

I may as well ask why wheels arent square. :rolleyes:

Mellor · 02-06-2020 02:00AM

Anaya Sticky Self-portrait wrote: »

Can we please stop with these type of nonsense answers. Are we in artic circle or Sahara desert?

They are the answers to the nonsense questions you are asking.
I mean, you are wondering why skyscrapers are not made of timber. Clueless stuff.

I've no idea what you are on about with Artic circle. Ireland varies more in temp that the artic circle.

02-06-2020 02:19AM

In a country with varying levels of wind, wood, which flexes is preferential over a rigid material like steel that doesn't flex.

A sharp gust against a rigid steel roof will lift the roof off, whereas a wooden roof in the same conditions would bend and flex and divert the wind away and stay in place.

Victor · 02-06-2020 05:57AM

Horses for courses - weight, cost and workability.

While steel is high strength, it is dense. To achieve the structure needed for a roof, the members would need to be disproportionately large and / or frequent, likely resulting in a roof that is overall heavier than a timber roof.

Steel is expensive.

It is difficult to work steel and can be prohibitively expensive to do so on site. It's a lot easier to cut 10mm off a piece of timber than to do it to steel. Similarly, if the holes in 2 pieces of steel don't line up, you're stuck.

Now, that said, if you want to build a building with large spans, e,g. a warehouse, steel is very useful.

Skyscrapers use steel more than timber because steel has a higher density and compressive strength.

hesker · 02-06-2020 12:59PM

Timber is a renewable resource.

Lumen · 02-06-2020 01:18PM

hesker wrote: »

Timber is a renewable resource.

So is steel!

hesker · 02-06-2020 02:11PM

Lumen wrote: »

So is steel!

Do you mean recyclable

Lumen · 02-06-2020 02:24PM

hesker wrote: »

Do you mean recyclable

You're right, I was sloppy with wording.

I suppose what I meant was "sustainable", in the sense that both timber and steel can be responsibly produced and recycled so as to cause minimal environmental damage.

In practice, it's way more complicated.

Ireland's spruce infection, for instance, is simplistically sustainable but ecologically grim.

And once you start assembling structures from timber you end up using nasty plastics, resins and preservatives to give the required performance characteristics (glulam, lvl, plywood, membranes, copper biocides...).

I am a big fan of timber and steel structures though. You can't get very far in a wood structure without steel.

v638sg7k1a92bx · 30-06-2020 06:00PM

muffler wrote: »

I may as well ask why wheels arent square. :rolleyes:

That would be a stupid question.

v638sg7k1a92bx · 30-06-2020 06:01PM

Victor wrote: »

Horses for courses - weight, cost and workability.

While steel is high strength, it is dense. To achieve the structure needed for a roof, the members would need to be disproportionately large and / or frequent, likely resulting in a roof that is overall heavier than a timber roof.

Steel is expensive.

It is difficult to work steel and can be prohibitively expensive to do so on site. It's a lot easier to cut 10mm off a piece of timber than to do it to steel. Similarly, if the holes in 2 pieces of steel don't line up, you're stuck.

Now, that said, if you want to build a building with large spans, e,g. a warehouse, steel is very useful.

Skyscrapers use steel more than timber because steel has a higher density and compressive strength.

Cost of timber is not that much different from steel atm.

GreeBo · 30-06-2020 06:04PM

Deleted User wrote: »

A sharp gust against a rigid steel roof will lift the roof off, whereas a wooden roof in the same conditions would bend and flex and divert the wind away and stay in place.

Ha?

Can you elaborate on this a bit?
Are you maybe confusing a steel clad roof with a tiles/slate roof?
The OP is about the structure of the roof, not the finish.

Victor · 30-06-2020 08:38PM

It would take an extreme event, but if something is too rigid, with no give, it can break instead of flexing. You could still make it rigid, but you would have to use more material than you would need otherwise.

Due to their relative lightness, most roof coverings will flex somewhat. If the structure is too rigid, there will be a variation in the flexing between roof covering and structure. Over time, this could loosen joints, fixings, etc.

Crumple zones in cars would be another example, although not quite the same. The crumple zone distorts, so the passenger compartment doesn't.

GreeBo · 30-06-2020 08:54PM

Victor wrote: »

It would take an extreme event, but if something is too rigid, with no give, it can break instead of flexing. You could still make it rigid, but you would have to use more material than you would need otherwise.

Due to their relative lightness, most roof coverings will flex somewhat. If the structure is too rigid, there will be a variation in the flexing between roof covering and structure. Over time, this could loosen joints, fixings, etc.

Crumple zones in cars would be another example, although not quite the same. The crumple zone distorts, so the passenger compartment doesn't.

Yeah I understand that, but I fail to see how timber trusses and joists would fair any better than steel in the scenarios you are talking about.

Steel flexes too and if timber flexes more, then that's asking for trouble where the roof meets the house surely?
Also the main goal is to keep the roof attached to the house in those extreme conditions, the stronger the structure the better imo!

The #1 reason is cost, both of materials and time to work with.

Mellor · 01-07-2020 02:08AM

Anaya Sticky Self-portrait wrote: »

That would be a stupid question.

exactly.

Victor wrote: »

Due to their relative lightness, most roof coverings will flex somewhat. If the structure is too rigid, there will be a variation in the flexing between roof covering and structure. Over time, this could loosen joints, fixings, etc.

What sort of roof covering/structure are you describing?

Tiles and slats for example are relatively heavy, and very rigid. They are fied in a way that allows movement between members, so that it copes with deflection in the structure (whether it is timber or steel). But there is no additional flex in the lining other than the structure.

The idea that steel is rigid and won't flex is simply not the case.

v638sg7k1a92bx · 01-07-2020 03:33PM

A lot of chipping and changing and cutting goes on with timber roof. Steel just slots into place.

Bonzo Delaney · 02-07-2020 05:14AM

Anaya Sticky Self-portrait wrote: »

A lot of chipping and changing and cutting goes on with timber roof. Steel just slots into place.

Maybe check twice cut once

Mellor · 02-07-2020 06:04AM

Anaya Sticky Self-portrait wrote: »

A lot of chipping and changing and cutting goes on with timber roof. Steel just slots into place.

Not really.
A prefab timber truss goes straight up, so does a prefab steel truss.
If you have to chop and change either, then you have messed up somewhere.

Obvious a timber cut roof is cut and measured on site. But so too would a steel cut roof be. You have to compare like with like.

maestroamado · 02-07-2020 06:16AM

Mellor wrote: »

Not really.
A prefab timber truss goes straight up, so does a prefab steel truss.
If you have to chop and change either, then you have messed up somewhere.

Obvious a timber cut roof is cut and measured on site. But so too would a steel cut roof be. You have to compare like with like.

The design of trusses means they cannot be chopped as the strength is in the design to spread the weight directly downward on walls.

Steel truss roofs are used for industry, factories and sheds.
I have not seen steel roof in houses...

Lumen · 02-07-2020 07:01AM

I'm not sure why more gabled houses don't use a steel ridge beam (and steel king posts,, if the house is otherwise timber framed), plus external (to the load bearing structure) roof insulation.

It solves the wall spreading issue without the need for ties, so had the potential to great incredible vaulted spaces, keep MHRV services inside the envelope etc.

Why are roofs on new builds made out of wood and not steel?

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