If you happen to enter a newer home one of these days and take a walk into the basement, then you’ll likely see joists that don’t look very familiar if you happen to look up. Why? Those are engineered wood joists, and they are increasingly taking the place of 2×10 lumber in joist applications. But when it comes to engineered floor joists vs. 2×10 traditional sawn lumber, the winner isn’t always clear-cut.
Engineered floor joists can span greater distances between bearing points than 2×10 traditional sawn lumber, but only if the joists are properly blocked. Engineered floor joists are more expensive than 2×10 lumber, but are much lighter and easier to handle.
One of the reasons engineered floor joists, particularly I-beams, are so common is that they can come in lengths of up to 60 feet and can be cut to length on the job site just like regular lumber. This is attractive because you may be able to achieve one single-span with engineered I-beams in a new build, whereas in the past, you’d need double the amount of 2x10s since they are limited by their length.
In this article, we’ll go over everything you need to know about engineered floor joists, including what they are, how they work, and installation details. We’ll compare them to 2×10 lumber in all aspects to give you a clear idea of exactly what type of floor joist will work best for your new home.
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What is an Engineered Floor Joist?
Engineered floor joists are joists that use engineered wood in conjunction with standard lumber to comprise a more lightweight yet stronger joist than just using traditional lumber. It is important to note that engineered joists come in several types, from the popular I-beam type to truss-style joists.
Engineered wood can be anything from plywood to OSB to any sort of particle or fiberboard that can be found in your local home reno store.
An I-beam engineered joist is composed of two different materials. The middle of the beam, the web, is OSB – orientated strand board – which is anywhere from ⅜” to 7/16” thick. The top and bottom of the joist, the flanges, are either 2×3, 2×4, or LVL with a dado cut lengthwise through the width of both to accommodate the OSB board.
A truss-type joist uses dimensional lumber – most often 2x4s and 2x3s – to create a truss web and is joined together using metal plates. These joists are pre-fabricated and are heavy. They can span longer distances than other joists but cannot be cut or trimmed once fabricated.
Truss joists are much more expensive than engineered I-beams. They are also substantially heavier, as they are all solid lumber plus metal plates. Although they can span further distances than I-beams, it often doesn’t matter as most houses are narrower than the long widths a truss can span. Trusses do benefit from having open webs, which allow for easy electrical, plumbing, and HVAC installation. I-beams do not.
- Both can span great distances
- Easy to manipulate
- Truss webs have cavities
- I-beams can be cheaper than dimensional lumber
- Little to no sagging over time
- Individual joists are more expensive the dimensional lumber joists
- I-beam webs have rigid restrictions for hole size and placement
- Truss joists are very expensive compared to other options
What are 2x10s?
A 2×10 is a piece of softwood lumber used for construction. The wood species varies, but your local home reno store will stock wood that is common to the forestry industry in your area. It could be spruce, pine, fir, redwood, or another similar type of evergreen. 2x10s are not that size. After milling and finishing, an actual 2×10 is really 1.5” x 9 ¼”.
For a long time, 2x10s have been the floor joist of choice due to their low cost, strength, widespread availability, and ease of manipulation. However, the low cost of producing fabricated wood products has made I-beams nearly as cheap as dimensional lumber.
Also, engineered joists can be made to nearly any length – 2x10s only go up to 16’. You can find 20’ or even 24’ lengths, but be prepared to pay. Big box stores will not carry those lengths, you’ll have to go to a lumber yard to find them.
- Widely available
- Easy to cut
- Lengths are limited in size
- Heavy to move around
- Can warp or bow
Engineered Floor Joists vs 2×10: What Is the Difference?
There are many differences between using dimensional lumber, such as 2x10s, and engineered floor joists. Below we’ll go over each aspect individually to determine the better option when it’s time to construct your next house.
The dimensions of a 2×10 are actually 9 ¼” by 1 ½”. Lengths run up to 24’ but are only commonly found up to 16’. Anything longer will require you to pay a premium and you’ll have to make some phone calls to find those lengths without any guarantee of finding them.
Engineered I-beams come in lengths up to 48’. They start at 16’ and go up in increments of 2’. Depths of I-beams start at 9.5” and go up to 16”. Widths are either 2 ½ or 3 ½” depending on the size of lumber used for the flange.
I-beam depths mimic the depth of standard lumber used in joists but can also get much deeper at up to 16”. The webs of I-beams are primarily ⅜” thick but can also be 7/16”.
Truss-type engineered joists are either 2×3 or 2×4 lumber. Depths of these joists can go up to 36”, but those would only be used in commercial or industrial applications. The widths of these trusses are the width of a 2×3 or 2×4. Lengths can go all the way up to 60’, or more and are specifically designed per project.
Common uses for 2x10s are floor joists and roof rafters. 2x10s are still the most commonly used floor joists in residential applications simply because they are still, on an individual basis, cheaper than any other option on the market.
I-beams are increasingly taking over in new residential construction. In new construction, it is cheaper to use engineered joists in some cases. For instance, it is possible to use half the number of I-beams compared to 2x10s since I-beams can span further with center support. Thus when traditionally you would use two 2x10s to span the width of your house, you could just use one long I-beam.
Floor trusses are engineered per each specific job and are therefore more expensive. As such, they are often not an economical choice when building a home or garage unless you are looking to span space that is exceptionally large. Engineered trusses are therefore mostly found in institutional and commercial settings or very large homes.
Installing 2x10s and I-beams are similar in many ways, as they both are spaced at the same intervals. However, there are some differences between the two that make each install unique, particularly pertaining to the I-beam’s different profile.
When putting engineered I-beams in, they’ll more than likely be resting on a block wall for main floor support. If they are resting on wood framing, then you’ll toenail the bottom flanges into the framing. In mid-span, you’ll either install an I-beam blocking along the support beam or “squash” each I-beam above the beam. Squashing means vertically sandwiching each joist above a beam with a 2×4, at minimum.
Some homeowners may opt to double up the joists and use a filler block to connect the two beams, which is usually a 2×6 or greater, depending on the joist’s depth. This greatly strengthens the joist and is useful in applications where lots of weight needs to be supported.
Installing 2x10s is similar to I-beams, except that 2x10s often only reach from the supporting wall to the main or a main supporting beam. Then another 2×10 spans the rest of the way, from the main beam to the opposite wall. Thus, the 2x10s are staggered by 1 ½” on each side since they overlap each other over the main beam to increase the bearing of each joist.
Each 2×10 is toe-nailed into place over the main beam and sill plate. Blocking can then be installed mid-span or elsewhere, depending on how long each joist is. Spacing, either 16” or 24”, of each joist depends on the span and anticipated loads of the structure.
Overall if you are constructing a new home, then using engineered I-beams makes sense. Instead of laying out two sides of joists if using 2x10s, you only have to lay out one row of joists as they’ll span from one wall to the opposite wall.
At the time of writing, a 2×10 costs, on average, around $30 for a 16’ length. An engineered I-beam of the same length costs around $40. This quote is for an I-beam that uses 2×3 flanges and is 9 ½” deep. If you want a 16’ I-beam that uses 2×4 flanges, then you may have a harder time finding it as it will be more expensive and is rated for much greater loads. Thus, the 2×3 I-beam flange is more common.
As mentioned above, in the new construction of a simple rectangular residence, you would use double the 2x10s as you would engineered I-beams. If this home was 30’ wide, then you’d have a main beam in the basement at 15’. You would then have 2x10s spanning each side. If these were placed on 16” centers and the house was 45’ long, you’d have roughly 34 joists – per side. That’s nearly 70 2x10s at the cost of around $2100.
If you used engineered I-beams for that same house, at the same spacing, then you’d only need 34 – total. The I-beams can span the entire distance from the wall to the wall. To span that length, you might need larger I-beams, so we’ll say each beam is $60. But even with the cost increase, $60 x 34, your total is still under $2100.
There are many, many different varieties of I-beam, however, and not all of them are as cheap as the one mentioned above. If you have greater loads to support, such as additional floors on your home, then a 9 ½” deep I-beam with 2×3 flanges may not work for you. If you need something larger, your price goes up and it might then be more cost-effective to use 2x10s. It just depends on the type of project.
You cannot cut or notch a flange on an engineered I-beam. You can cut holes in them as you would in a 2×10, but the rules are more strict for where you can and cannot cut. For instance, you can place a hole anywhere within a joist web as long as it is ⅛” from a flange. You can also make a hole of 1.5” in diameter anywhere in the web, but must be double the diameter in the distance away from the inside of the next hole.
Generally speaking, the greater the distance from the outside edge of the I-beam joist, the greater the diameter of the hole you can have. Consult a notch table to determine the diameter of the hole you can cut based on the length of the I-beam you have. Typically, the maximum diameter you can cut in your I-beam is roughly ⅔ to ¾ the depth of the joist.
You can also make rectangular holes in engineered I-beams, but the long side can’t be more than 75% the length of the diameter for a round hole allowed at the same point, which your notch and hole table would indicate.
For dimensional lumber joists, such as 2x10s, the IBC states that you can’t have any hole within 2” of the joist’s top and bottom. You also can’t have a hole diameter that is greater than ⅓ the depth of the joist. You can have notches, but they must be no more than ⅙ the depth of the joist. Notches also cannot be within the middle third of the joist.
Thus, the rules for holes seem to favor engineered I-beams, as they allow larger holes – even rectangular holes – as opposed to 2x10s which only allow diameters that are ⅓ joist depth. Thus for similar-sized 2x10s and I-beams, you could have double the size hole in an I-beam versus a 2×10.
To get an idea of how far dimensional lumber, such as a 2×10, can span in floor joist applications, then check out a span table to see how far each width of lumber can span end to end. A 2×10 at 16” on center spacing can span 15’5”. Engineered I-beam span tables indicate that a 9 ½” deep I-beam can span 18’.
One thing to note is that the beam span tables for engineered joists also include a span table for “multiple span”. This is for joists that will be supported in more than two places. However, this can also include joists that only have two bearings but are also blocked or bridged properly. Thus a single span of an engineered I-beam joist for the dimensions mentioned above – 9 ½” deep and 16’ long – is only 16 ½’, but 18’ for multiple spans.
The more you increase the size of your I-beam, whether it’s the flanges or the thickness of the OSB web, the greater the span length becomes. Every manufacturer has many different types of I-beam joists, and the depths of these joists can go way beyond 9 ½”.
As long as you abide by the limitations set out by the span tables for your specific joist set out, then you are safe to walk on and live on the joists you’ve installed. Be sure to pay attention to loads, as some span tables are for a 40 PSF live load, and others are for 50 or more PSF.
Also, pay attention to the bearing of your joist – that’s how much surface area of the joist rests on the wall or beam the joist sits on. If your joists are bearing only an inch or two on the bearing area, then it won’t have the same load-bearing capacity as it would if it was sitting 3” or more on the bearing members.
The limits of the load tables are designed to be just that – limits. For joists, overbuilding is never a bad idea as they are one of the main supports of your home. While they are unlikely to collapse outright, ensuring your floors don’t wobble at the outset will save you lots of pain and effort later on down the road.
You can always make your joists safer by blocking or bridging your joists, abiding by the rules for notching and holes, fastening the joists properly, and keeping everything dry.
Lastly, it should be noticed that engineered I-beams are more of a fire safety hazard than traditional lumber. That isn’t to say I-beams are more likely to catch on fire than, say, a 2×10, but rather if there is a fire somewhere else in the house, an I-beam is more likely to collapse than solid lumber due to the OSB webs.
From a sustainability standpoint, many large lumber manufacturers will gladly tell you that their engineered products are nearly as sustainable as their standard lumber products.
This is a complex issue, but consider the type of lumber required for an I-beam versus a 2×10. You need a much larger tree to produce a 2×10. 2x3s and OSB can use much smaller trees. It is much easier for a lumber company to produce engineered lumber, relying on less material, as it is more readily available. Then they can re-plant their forest and harvest it in less time.
Therefore it might take more CO2 to harvest a tree for traditional 2×10, but the frequency of the harvest would be less. The real issue here is profitability. It isn’t sustainable for companies to rely on trees that produce 2x10s, so they invest in technology to mass-produce engineered wood products. They’ll never be as sustainable as regular lumber, but it is the way of the future.
Engineered Joists vs. 2×10 Solid Sawn Lumber: Which is Better?
While the dimensional lumber versus engineered joists is a close race, we suggest that an engineered I-beam floor joist is a better choice. The engineered wood ranks better in both cost, strength, and ease of installation. They are also very versatile and can have larger holes than a 2×10.
If you are simply looking to replace or sister some 2×10 joists in your home that are regular lumber, then you’ll have to use the same type of joist. Engineered floor joists are not meant to be used in tandem with traditional 2x10s.
However, if you are starting fresh and building a new home or structure, then I-beams are the best option. They are easier to handle and much lighter, plus they won’t bend or warp – no more wrestling bowed 2x10s into line as the engineered joists are always straight and true.
Whichever style of the joist you choose, just make sure to follow the span tables to the letter and overbuild slightly – you’ll never regret spending a bit more to have the peace of mind that you made your structure more solid and safer than required.