I-Beams: Wood vs Steel. Which is Best?

So you’ve decided to build an addition or learned that your home’s support beams are no longer doing their job properly.  What material do you use?  What do you do? It’s highly recommended that you hire a structural engineer and a professional contractor, but if you’re determined to complete the project or have the skills; Tim Carter, ‘Ask The Builder’, has some tips.

Recently, Tim Carter was asked by a reader of his column the following.

Question: I’m getting ready to build a large room addition that needs a beam to support the floor joists.I’ve been told that a wood beam will work, but I’ve always seen steel I-beams in other houses.  Is it possible for wood to do the job?  What are some of the pros and cons of wood I-beams and of steel?  If you were building, would you use wood or steel?  I don’t want to make a mistake on a such a critical structural element.

Answer:  Oh, gosh, there’s no easy answer.  both wood and steel can make fabulous load carrying beams.  I’ve used both materials for decades in all sorts of situations.  In fact, you may not realize this, but you can mix the two making a hybrid beam of wood and steel.

First, let me tell you that I am not a structural engineer, although I have worked with many and installed the beams they’ve designed.  The good news is that both wood and steel can be used to carry tremendous concentrated loads.

in the last house I built, I had two wood beams in one wall that supported tons and tons of weight.  in the basement of the same house, I had large steel I-beams that spanned 16 feet, supporting enormous loads as well.  The use of steel allowed me to create wide-open spaces with minimal port columns.

That is one advantage of steel over wood when you’re working with materials that are roughly the same size.  Pound for pound, steel is much stronger than wood.

What’s fascinating is to see the evolution of engineered wood beams over the past 40 years.  Laminated beams, mircrolams and so forth are very common now, but I clearly remember when they were brand new.  It’s not uncommon to find laminated beams in ordinary homes in today’s marketplace.

Go back in time and look at old barns and other buildings built using the post and beam method, and you’ll see wood beams made from one solid piece of timber.  Perhaps the strongest wood beams made this way are Douglas fir.  There may be a stronger wood, but I’m unaware of it.

Today, lumber mills make beams like the make plywood.  They use layers of solid wood that are glued together to make incredibly strong structural engineered timbers.

Keep in mind there are few cons to either of the materials.  I say this because you can usually have an engineer come up with a wood beam that can replace a steel one.  It’s all a matter of cost and the finishes dimensions of the material.

If you want to think of worst-case scenarios, think about the things that attack and weaken beams.  Water can rust steel and rot wood.  You can paint the steel beams with a primer and finish coat to build water resistance.  You can also have steel beams galvanized.  Wood beams can be treated with borate chemicals to minimize wood rot and prevent infestation by wood detroying insects that can’t harm steel.

If you want to fasten somehting to a steel beam, it’s a challenge.  You can easily nail into a wood beam or drill through it properly to install a bolt.

You can create a hybrid beam using a steel flitch plate that’s sandwiched between two regular pieces of wood framin material.

The flat steel plat usually has staggered holes punched in it and you bolt the wood and steel together to create a super-strong beam that might carry a load four or five times greater than what the wood could carry in the same space.

Fire is a danger to both materials.  What fire does to wood is well known, but heat from a fire can also weaken a steel beam, turning it into soft taffy.  You can wrap a wood beam with fire-resistant drywall to protect it and commercial fire protections can be sprayed on steel I-beams.