Gaps Between Hardi Plank Siding

Leave a 1 8 gap between the siding and the trim or other materials to allow for structural movement.

Gaps between hardi plank siding.

Vertical trim gap caulking. Remember that most hardie siding problems are caused by improper installation. Do not caulk between siding and any built in receiving channels located at or around windows. In contrast caulk manufacturers specify a minimum gap at butt joints which can become more visible as the caulk ages.

If siding butt joint gaps are due to shrinkage the central problem is one of shrinkage that occurs principally if the siding was not stored properly prior to installation particularly if it got wet. Always prime or paint any cut edges that are inserted into a window j channel. Run the siding to the hardietrim board leaving a 1 8 in. James hardie recommends the use of caulks and sealants that remain permanently flexible.

High moisture at time of installation is going to give gaps. The boards would shrink a little bit making the gap 3 16 to 3 8 depending on how much moisture was in them and how close the install gap was to 1 8. Always caulk between the siding and the trim. This is a common mistake and so easy to avid.

10 years ago the installation directions called for an 1 8 gap and then caulk. When james hardie siding products butt into wood based materials a 1 8 gap will allow for expansion and contraction of the wood based product. It is also difficult to achieve the specified gap in the horizontal overlap. 16 or 24 on center let in bracing weather resistive barrier fastener 1 4 thick lath strip moderate contact or maximum 1 8 gap.

Double wall construction single wall construction. James hardie recommends butting field joints together in moderate contact to achieve a continuous looking joint. During my time working for james hardie i very rarely got calls from homeowners that wanted to submit a warranty claim for their hardie siding. 3 8 from plank edge leave 1 8 gap between plank and trim then caulk weather resistive barrier plywood or osb sheathing.

James hardie recommends the use of caulks and sealants that remain permanently flexible. Flashing installed incorrectly or siding installed without the proper gap between the siding and flashing will both result in water damage and a voided warranty. Hardie siding requires a minimum 2 gap from all hard surfaces like decks or rooflines and at least 8 from any soft surfaces like grass dirt or gravel. Gap between the siding and trim.

But the siding should never hang below the trim.