Does Hardiplank Require caulk at the joints?

I’ve always seen the joints caulked…until this past Saturday. A 3000 SF house had not one speck of caulk at the end joints (it was caulked at the trim).

The instruction state: “James Hardie does not recommend the use of caulk at field butt joints.”


I had the same situation a few weeks ago and the hardiplank site said DO NOT caulk butt joint. Here is the link:

Note the photo of a special flashing required behind the butt joints. Not sure how the code inspector, or I, could verify the flashing.

HardiePlank Installation.jpg

Caulking is one of 4 ways James Hardie recommends handling vertical butt joints of non-colored 4’ X 8’ sheets.

4x8 sheet? I’m speaking about traditional lap board.

They have changed their installation requirements over the years. Used to be standard to caulk, now they say no. I always caulk field cuts but if there is a good installer, those cuts will be next to a trim board that will be caulked anyway. I use 30# felt in back of the joints. If you run a thicker sewing pin down between the two pieces, you can feel if the flashing is there.

Joe, I think your image is specifically for ColorPlus where they don’t recommend caulking.

For regular Hardiplank lap siding (the kind you paint AFTER installation), caulking at butt joints is optional. This from installation instructions:

As a side note, it’s been my experience that it isn’t worth paying for the ColorPlus stuff because it gets all scratched up during installation and you’ll have to re-paint it anyway.

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Having done many of these instalations, I could not agree more. Even the cuts make the job look poor. Good advice Nick.

I will second that Nick, Having installed it. It does allow you to one coat finish though.

Thanks Joshua Good explanation… Roy

Yes Josh.
Flashing is the weakest link in all the building trades. From electrical to hardboard installers, slate repair roofer to patio and deck installer at the sill plates.
The old-school hard nosed teachers are fewer and farther between.:mad:

Apparently no one here read the technical bulletin #9 that James Hardie released in 2008. Hardie no longer recommends the caulking of any joint in their lap siding (colorplus or primed). Deterioration of the caulking in the joint has become a maintenance issue for home owners over time. Joint flashing is recommended for all hardie lap siding now. Although I do not understand why they have not changed the information about caulking in the instruction manual.

It is shown in their Installations now.

Here is a picture;

Picture courtesy of;


I think personally with the different methods of install on this product from what I have read about it. I would be more concerned with uniformity of install.

If I had some joints caulked and some not, or found evidence of flashing only behind certain parts I would call out incorrect installation.

I agree with Marcel, Caulked butt joints are a maintenance headache for homeowners. This material moves a lot and caulks just do not hold up. Flashing of the field butt joints is the best way to handle it.

I still see many contractors out there who are caulking they should not be.

Agreed, flashing field butt joints.Although I have never seen caulked butt joints, I could imagine it would be unsightly. The expansion /contraction would cause visual distortion in the caulk at the joints I presume…
Dam the new windows pro two has small front. Time to adjust the size.
Sorry all.

Caulking or not, I would do the flashing, it’s a thing of beauty. I love finding a builder with well done flashing details. Does NACHI have a course just on flashing throughout the exterior? That would be a great course.

I think they should as well.
Bravo, an idea like minded inspectors can convey to InterNACHI. Nick I think Cameron just developed the next InterNACHI course.