Algae growth on vinyl siding (C) Daniel Friedman Vinyl Siding & Trim FAQs
Diagnostic questions & answers about vinyl siding & trim

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FAQs on how to install, remove or repair vinyl siding & trim on buildings:

This article provides answers to many questions about vinyl siding installation, how to remove vinly siding, how to repair vinyl siding & how to diagnose buckling, cracks, breaks, or stains in vinyl siding on buildings.

In this article series we offer specifications for installing vinyl siding including corner posts, fixture mounting blocks, use of J and F channel, nailing guidelines, horizontal overlap, trim details and options, and how to assure proper waterproofing at a vinyl-clad building.

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Vinyl Siding FAQs: siding installation, leaks, buckling, stains, removal & repair

Vinyl siding nailing flange (C) Carson Dunlop AssociatesReader Question: Working With the Local Building Code Officials, Building Inspectors, & Building Code Compliance

Can I install the vinyl siding on my garage apartment project before I install drywall. - M.A. 9/21/2013


Your question is worrisome - as I'm not sure what you are worried about. Exterior siding has nothing to do with interior wall finish materials, except that it would be foolish to install interior drywall, vapor barriers, or insulation in wall cavities before the building exterior is finished sufficient to be completely weather tight.

Reader follow-up:

The building inspector is concerned that weight of drywall will cause siding to buckle.  9/22/2013

Thank you for the information on vinyl siding installation.  I was not worried about installing the siding it was the building inspectors  concern  that if  the siding was installed prior to hanging the drywall  that the weight of the drywall would cause the siding to buckle. M.A. 9/23/2013


I'm sorry, but with respect, I can't make any sense whatsoever out of the concern you describe.

Drywall is attached to and supported by the building structure not by the vinyl siding.

In proper construction we complete the building shell at least far enough along to make the building waterproof before we would ever consider interior work such as installing insulation and then drywall on walls and ceilings. The building may be dry - weatherproof, once the roof is on, wall sheathing is on, house-wrap is on, windows and doors are in place, and probably most exterior trim is in place; at that point the shell should be dry and weatherproof (unless an idiot installed the building housewrap improperly) and both exterior siding and interior work (wiring, plumbing, insulation, drywall) can proceed.

I suspect there is a serious miscommunication going on here.

Reader Follow-up:

As I am very limited with computers please excuse my inexperience. I thank you for all the information regarding my 2 story garage apartment project. I have never thought it was a problem to install the vinyl siding prior to installing the dry wall. It was the building inspectors concern. I would love to get my home sided before winter so that I could start the inside. Can building inspector force me to wait or can I move forward with my vinyl siding installation. Thank you again. - M.A. 10/17/2013

Reply: how to get along with the building code inspector: comply with the building codes

Can the building inspector stop a construction project?

If by building inspector you mean the local town or city building department's inspector: yes absolutely that person can stop a construction project.

But in the case we have been discussing it sounds to me more as if there may have been some confusion about just what the problem is.

In my experience, building department officials are sick and tired of people who are trying to evade proper construction codes and practices and not very friendly to people who they think are trying to do something cheap, stupid, or similar.

But if the inspector understands that you want to do what is correct and proper and you fully intend and want to comply with the building codes and officials, you can usually expect the building inspector to be "on your side" and even to help you out by making clear exactly what they think is required.

If then you think what the inspector has said makes no sense, you need to get the requirement clarified; on occasion the building inspector may agree to a variation from what she or he has specified if the variation in turn has been signed-off-on by a licensed building professional such as an architect or engineer. In that case they are passing responsibility for correctness and safety on to that person.

It might help sort out some of the confusion about when you can hang vinyl siding and when you should or should not hang drywall by reviewing the concerns listed at DRY-IN, DEFINITION. There you will see that weight of the outside or inside wall claddings is not listed.

Frankly I cannot imagine that a knowledgeable building professional would want the (insulation and) drywall installed before the building exterior shell is dry - which would normally include the steps I described above. Installing drywall presumes that we have already installed wiring, plumbing, and building insulation first. If those were installed before the building exterior were fully sealed against the weather we are inviting a catastrophe: leaks into the building walls, wet insulation, mold, rot, insects, a disaster.

That's why I said earlier I thought there must be a misunderstanding. In general in construction we frame the structure, then install roof sheathing and roof covering and wall sheathing, then house wrap, then windows, doors, and exterior trim; When those components are in place it is perfectly fine to install the finish siding outside, even if the walls have not been insulated; In fact the more complete that we make the exterior shell of the building the more we are assured that the building is "dry" - which makes the installation of wiring, plumbing, and then insulation safe - in that we don't want wiring or insulation to be wet.

Watch out: some building departments permit drywall to be installed before the building dry-in has been completed provided that moisture-resistant board (presumably greenboard or cement board) is used on the building interior surfaces. In my OPINION this is very risky - wind-blown rain or any other leaks entering enclosed (and worse, insulated) building wall or ceiling cavities is an engraved invitation to possibly dangerous and certainly costly mold contamination that may not be discovered until later. Such problems can be initiated in as little as 24-48 hours after a wetting event. Longer term problems may ensue such as insect infestation or even rot.

Keep me posted and send along photos of your project if you can - that may allow further comment.

Question: I need to replace a vinyl corner post but can't find a match

I need to replace a vinyl corner post made by Bird & Sons. The post is light grey, 3 1/4" wide with a " smooth " surface. I found that finding this item is a real bear. I've been looking up Bird & Sons on the net for possible help but find it is over welming for me to make heads or tales from all the stuff posted. Would you , if you can, shed some light on this item? - Rick Lupold 7/12/12



Your best bet is to find the closest match to the original siding in color, putting texture secondary, from another manufacturer. In my experience, especially with older vinyl siding, even if you found an "exact" match by product number and brand, age and sun exposure will have changed the color of the siding on the building so the new part won't exactly match anyhow.

The worst problem is not matching the color, it's the amount of siding that you'll have to pull off to remove the old and nail the new corner trim in place.

Question: diagnosing why there is rippled odd looking vinyl siding

The picture with the dryer vent below the window [we moved it to collect related info together - see Buckled, Rippled, Deformed Vinyl Siding Caused by Other Hazards: heat leaks, chemical spills, unknown] was caused by the reflection of the sun off the window. I would put $$$ on it. - Jim Hilt 9/11/2011

There's a good chance the rippled effect on the siding was caused my improper dryer vent installation and hot dryer air is leaking behind the siding. - Anonymous 9/15/2012


Thanks for the guesses, Jim and Anonymous. Working together we are smarter than working alone.


But in this case, while I thought you might have something there, after a more careful check, I don't think so. Look at that photo again carefully - you'll see that the rippled vinyl siding extends way below the opposing window - not in the path of reflected heat from the window glass.


We have expanded our discussion of the rippled vinyl siding effect to explain the difference between obvious heat damage from a barbecue grill and the odd rippling in our photo above. The vent you saw is not for a hot air dryer, it's an air intake for a fireplace insert built into that chimney chase. But your guess is a good one in that there may be a more dangerous hot gas leak from the fireplace. For that reason we recommended invasive inspection to check the chimney chase interior as well as the condition of the fireplace

For additional photographs and discussion of all types of sagged, torn, cut, broken, rippled, or otherwise damaged vinyl siding, take a look at the companion article VINYL SIDING INSPECTION & REPAIR and within that article see these subtopics

Question: vinyl siding installed over asbestos cement shingles

(Mar 20, 2013) joseph bonell said:
When i got rid of old asbestoes siding i had new vinyl siding installed under half in. insul.and under that the old brown fiberboard.I thought of having the old fiberboard replaced with wood,for better strenght,somewone can cut there way into my house,anyway vinyl sideing is not maintanence free ever other year it seems i have to pressure clean it,mold,anyway to prevent this growth,paint or wax? x



If you are having to pressure clean your new vinyl siding every other year I suspect that either your home is close to a dust source (road, highway, industrial activity, farm) or one or more sides of the home are quite shaded, giving problems with algae formation.

I am not sure what you can do about dust settlement; if the problem is algae or fungal growth on the siding, trimming back trees to increase sun a bit can help reduce shade and dampness.

I would be very careful about power-washing siding to be sure to spray "down" and away from window and door J-channels. Otherwise you risk blowing water into the building walls, creating a mold problem therein.

Wax doesn't seem sensible to me nor practical and may in fact attract and stick more dust. But do consider using a mild detergent or deck washing solution when cleaning.

Question: wind damage to vinyl siding, no house wrap

(Mar 28, 2014) Anonymous said:
We have had to have vinyl removed and repaired on one side of our home because of high winds coming through. We are no longer loosing siding but there are small gaps between some of the vinyl pieces. Does this problem create a chance for water damage or mold underneath the vinyl? Also what type of underlayment should be put underneath the vinyl? When the vinyl was taken down there wasn't any underlayment, the plywood was exposed. Will this create a problem over time, and does it create any other problems? Thank you for your help. Ayn


Yes Ayn, gaps invite leaks into the wall structure, leaving the building dependent on a perfect installation of water-resistant house wrap to avoid future rot, mold or related water damage.

Siding gaps are an improper installation.

In the More Reading links above click on the article titled



See our home page on vinyl siding inspection & defects lists at

for more details about gaps in vinyl siding.

Question: using screws to secure vinyl siding window trim?

(May 13, 2014) Jean said:
I'm having VS installed and the contractor is screwing the vinyl window trim in. The screws are not concealed and he said that's the only way to do it. Is this a common way to do that? It looks tacky to me.

**Edit** Sorry, I need to clarify my 1st post. My contractor is using wide window casings instead of J channels. He is putting screws on the in the corners, on the outside of the casing.This doesn't seem right.


**Edit** Sorry, I need to clarify my 1st post. My contractor is using wide window casings instead of J channels. He is putting screws on the in the corners, on the outside of the casing.This doesn't seem right.

Question: J- Channel leakls in winter - can I fill the J-channel groove with caulk?

(May 26, 2014) Anita Grant said:
I have a deck which is a roof to a room. I had my house redone in cedar shake ginyl siding and j channel was used above ice and shield roofing to keep water out. This winter which was very snowy some water got in. Not much. Can I fill the j channel with caulk to make it more waterproof.



I'm doubtful that filling J-channel will help you but I confess I don't have a clear picture of the design you describe.

J-channel is used normally around vinyl or aluminum siding at windows, doors, at building corners and at soffits to receive the butt-ends of siding. Using J-channel in any way in a roofing application is not something I understand.

You can use our CONTACT link to send sketches and photos - that might help.

Question: solving leaks at J-Channel around windows with vinyl siding

31 jan 2015 kennyG said:

This job was vinyl siding installed over the old wood siding. J-Channel was rapped around the old wood window frames which were then wrapped in aluminum. Water was entering the building between the J-channel and the old window frame. To correct the problem the installer used clear silicone caulk to fill the small gap between the window frame and the J-rail. My concern is that water can no longer exit under the j-rail at the top of the window because this is now caulked. Please advise if this caulking is an accepted practice. Thanks.



Best practices when installing J-channel include:

- house wrap and window flashing properly installed around windows before siding is installed; if these were omitted all bets are off

- the J-channel is cut long over the window top and then its ends cut so as to permit bending the extensions down over the outside of the vertical J-channel so that water entering the horizontal J-channel, when it runs out of the ends of that section, is directed outside rather than inside the wall.

If the J-channel was properly installed one would not expect to need to caulk between the J-channel and the actual window trim.

If the J-channel was not properly cut and installed, it MIGHT be possible to fix leaks with careful strategic application of silicone caulk to cleaned surfaces. I dunno. Your description sounds as if a big blob of sealant was installed at the J-channel ends. You'll need to look to see where water now goes if it overflows the J-channel rather than running out at its ends.

Our email is at the CONTACT link at page bottom - send me photos for further comment.


(Mar 19, 2015) ellen said:
Can an exterior roller shade be installed on a vinyl siding patio roof


Sorry Ellen I don't understand the question. Vinyl siding is on building walls. A patio roof is a different structural component.

Question: how to seal a hole or rodent entry point in vinyl siding

(May 13, 2015) JP said:

What do you use to fill the hole when they installed central air. The stuff covering the hole has dried out and mice are getting in the basement and nobody seems to know what to replace it with, could you please help

The stuff covering the hole has dried out and mice are getting in the basement and nobody seems to know what to replace it with, could you please help



Steel wool is a great mouse deterrent at building openings. Use that in the opening, covered with sealant and if necessary flashing to keep weather and water out of the building wall .

Question: I found carpenter ants behind my siding - how do I fix the problem

After i took down insulation i found a lot of carpenter ants ,killed them . investigated more around the house noticed in the garage that there were more took down sheet rock water damaged. j channel cut and holes with wood showing .how do i fix this? - Dale 7/21/12


Dale you're going to need to follow the water backwards until you've found the leak or water entry point; fix that, and restore the siding; You'll need the "siding hook" siding replacement tool we describe if you're working from the bottom of the wall up.


Question: snow damage to vinyl siding ?

(Apr 21, 2014) Anonymous said:

Does snow accumulation against vinyl siding cause any damage to the siding?


Snow is unlikely to damage vinyl siding. However, melting snow piled against vinyl siding means there is a risk of water penetration into the wall structure - which could be a source of damage: rot, mold, pest infestation.

Question: vinyl siding sealed to concrete slab

(Oct 24, 2014) Pausha said:

The brand new house that we are planning on buying, has the vinyl siding sealed to the very bottom to the concrete slab by mortar. Is that right? Our home inspector thinks that it should have some kind of gap for the water to pass, to avoid water damage. Thoughts?


Pasha your home inspector was on target. Clearance space is to avoid both rot and insect damage.

Question: rain rots door frame, where is the leak?

(Nov 24, 2014) Fred said:

I have a side entrance door to the garage. Rain water is rotting the bottom of the door frame on the hinge side. Where can this be coming from? I already replaced the door frame once.


Fred, that sounds as if there may be both door head flashing and side flashing errors and framing or trim details trapping water in the structure.

Question: siding falls off the house or is easily pulled off

12/11/2014 Amanda said:

Hello. We had vinyl siding installed and now peices have falled off or are bowing out. We had a friend come over who we found out does it as well and he ended up placing two fingers under the siding and pulled and it popped off. IS it supposed to do that?


NO Amanda certainly not. It sounds as if siding on your home was nailed to some sort of soft sheathing such as fiberboard and it missed the wall studs. Better ask an experienced siding contractor to take a look to see what's needed before more blows off.

Keep us posted. Send along photos if you can (see our CONTACT US link) and I can comment further.

Question: cut off the vinyl skirting around a mobile home to cure buckling?

(Jan 2, 2015) ml said:
My mobile home has sunk due to standing water. We put in gutters and that helped. But I don't have separate skirting. The vinyl siding covers everything. The part of the siding that touches the ground is bending inward. Can it be cut or sawed off to stop the pressure? If not, then what. I'm not loaded with cash. We have had it leveled this year by a person I know is responsible.



The idea of sawing off the plastic mobile home skirting is probably missing something more important: the home is sinking; we need to identify the cause and fix it. I suspect that the home was never placed on a concrete slab with a footing nor even on properly-constructed masonry piers. Perhaps it was just set on concrete blocks placed on the ground.

WATCH OUT: a sinking mobile home can break gas lines, plumbing piping, and can tear electrical wiring - any of which can be quite dangerous.

The proper approach is to inspect and repair the supporting piers for the home, if necessary temporarily adding support until proper piers can be built. Inspect the connections to any piping, wiring, etc. that may have been moved or damaged and have any damage repaired.

Quite possibly jacking and leveling the home to get it properly supported will actually result in the home being lifted up a bit - so do not cut or trim any skirting until all of the proper repair work has been done.

Details are at this article about proper support beneath mobile homes


Reader Question: how to flash vinyl siding where it abuts a concrete slab

Question: How to install siding down to concrete slab

I have a closed-in patio with a concrete slab that extends beyond the external patio wall. I'm replacing the old cedar siding with vinyl siding and was wondering what the 'right' way is to install the bottom edge of the siding (directly on top of the slab). The wall sill plate is a pressure treated 2x4 sitting on the concrete slab. Should I use a j-channel (nailed to the sheathing and caulked to the concrete) to hold the bottom edge of the siding, or should I use a starter strip and leave a gap (maybe 1/2") between the siding and the slab, which would leave the sill plate more exposed? - Bob March 2015


Bob I never like to take siding right down to a slab without first understanding how we're keeping water out of the wall at the slab-wall juncture. I've seen building wall rot at just that point. My solution was to chop off the bottom 12" of a wood framed wall, install a solid concrete block sill, atop the sill a sill plate to which the wall studs connect; with 4" or more of solid masonry sill above the slab, I could then bring siding down just over the top of the sill plate an inch or so.

Some flashing details from our article by Steve Bliss are at


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