Old-School Craftsmanship, With A Modern Touch!

What Contractors Get Wrong With Hardie

March 30, 2022

Three Things Most Utah Home Contractors Get
Wrong When Installing James Hardie Siding

And Why Those Mistakes Could Doom
Your New Home Siding Project

Nothing protects your Utah home like James Hardie fiber cement siding – when it’s installed correctly.

But when your contractor cuts corners, you can end up with a disaster on your hands.

There’s a reason that James Hardie siding comes with a 130-page installation manual. Their siding is more than slats – it’s a carefully engineered system that needs to be installed with care. If you skip a step, you may as well skip them all because the results will be the same.

1) No Flashing Installed

Flashing is any material installed to prevent water infiltration at any seam. We take things a step further and use metal flashing instead of the less expensive cloth allowed by the installation instructions.

We use metal because you can get a better color match, and the powder-coated metal will never fade. It also won’t tear at the nails and fall out of position as cloth flashing can.

Unfortunately, many contractors don’t even bother with flashing when installing James Hardie siding.


They are either trying to save on materials and labor, or they just don’t know how to get it right. Either way, they are setting your new siding up for eventual failure as water is allowed to reach the cut ends of the slats.

Once water seeps into those unprotected ends, the slats will start to swell. And when you call Hardie to use your warranty, you’ll find that they don’t cover issues arising from improper installation and deny your claim.

2) Using The Wrong Trim

One of the nice things about fiber cement siding is that its expansion and contraction rate is essentially zero. Even in extreme conditions, fiber cement simply doesn’t change dimension – ever. So it’s important that the trim you use doesn’t move either.

With that in mind, you need to use either fiber cement or metal as your trim material.

But wait, doesn’t metal expand and contract quite a bit? Yes, it does. But when you use metal trim, the slats lay behind the trim in a channel, so movement isn’t an issue.

Problems only show when you use vinyl or wood trim. Their comparatively violent motion against the fiber cement slats in changing temperatures prematurely ages and cracks the caulk.

And since the contractor willing to put on the wrong trim probably isn’t using the best caulk, that aging can happen quickly. Within just a few years, you’ll be calling up Hardie to complain about your siding.

And, once again, they’ll look at the installation and deny the claim, leaving you with a growing problem that will take thousands to solve.

3) Failure To Prep Your Home

One expense that homeowners and some contractors are always happy to avoid is the cost of demoing the old siding. Sometimes homeowners want to keep the old siding on as additional insulation.

Saving money isn’t necessarily a bad thing, but it needs to be done with thought. If the old siding has a lot of ridges, installing the new siding on top can cause issues.

So, we’ll only agree to leave the old siding on if it is a fairly flat surface, such as lap board siding, and only if it’s in good shape. Nobody wants new siding supported by a crumbling surface.

But some exterior home renovators care only about speed, and leaving the old siding up can save them a full day of work. If the pattern of the old siding is particularly uneven, they’ll put a foam layer over the old siding. But even then, they aren’t considering the potential for problems, such as:

  • The Quality of the Surface Underneath – the chance of a contractor that cuts corners looking at the substrate behind the old siding is slim. But the chance that the substrate is dried out, rotted, or otherwise weakened is high.

    So you can put in all the nails you want, and you’ll still not have a strong connection between your new siding and your home.

  • Proper Nail Length – when you put foam over the old siding, you’re adding another half-inch of depth to get through. Now you have a half-inch of new board, a half-inch of foam, the thickness of the old siding, and the space between the old siding and the substrate to cross.

    That last measurement is unknowable because it will change from spot to spot. So if you guess wrong, you can end up with beautiful new siding held in place by nothing more than the foam and the old siding, which is not a good thing.

  • Bent or Blown Through Slats – if you accidentally place a nail over a gap behind the foam or old siding, that extra bit of depth can cause the slat to bend inward or the nail to just blast through the board. Once that happens, the slat is ruined, and if it happens once, it’ll happen all through the build.

Getting James Hardie Siding Right

As we said above, James Hardie siding requires careful to the letter installation procedures. The best approach is to start with a clean slate

That means you remove the old siding and check all the walls (substrate) for a good, quality work surface that will hold your nails tight. If you find problem areas, take the necessary steps to get them up to snuff.

Once you have a nice, even surface to work with, crack open the book that Hardie calls their installation manual. Then, do exactly what it says with the materials they tell you to use (unless you take it up a notch like using metal flashing), and don’t deviate from their instructions.

If your contractor does that, you’ll have great-looking siding for the rest of your days.