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UnderDeck Common Questions

We’ve gathered the most commonly asked questions about UnderDeck. If your question isn’t answered here, you may also contact us with any questions you may have.

Installation Questions

How long will my installation take?

It depends on the size of the deck. However, it should not take more than 4 hours on a typical 12'x12' deck. Normal installations estimate 50 square feet per hour per two person crew.

I am a good handyman. Is this product too much for me and a friend to install?

This product is specifically designed to be installed by individuals who have not installed it before. Some homeowners have to rely on their trusted builder or a contractor they know to perform the installation. Simply read the Installation Guidelines section to fully understand all the details of the installation.

If I need help or have technical questions, who do I call?

FehrMark Technical Support for UnderDeck can be reached at 888.353.3347. They can handle all of your questions from their Technical Support Center (Monday-Friday 8am-5pm CST).

Can the UnderDeck System be attached to my existing deck?

Yes, UnderDeck can easily install to virtually any existing deck. Let us know about your specific project and we will assist you.

Can I install UnderDeck system myself?

Yes, you can install the product yourself.

What type of sealant do you recommend for around the Water Diverters?

FehrMark recommends UnderDeck is sealed with a tri-polymer product that is made by Geocel. It applies in all weather – even on wet and oily surfaces. Menard’s has it private labeled under the brand ULTIMA – window, door & roofing sealant. It is similar to a silicone sealant.

Can I paint the UnderDeck?

Yes, you can paint the UnderDeck. However, painting the product does void the manufacturer's warranty. Your local home center should be able to recommend an exterior paint for use on vinyl.

The joists on my deck go the opposite direction to the ones in the instructional video. Can I still install Underdeck?

It's fine if your joists are in the opposite direction than in the UnderDeck Installation Video. Underdeck will work fine in this scenario. You can treat one of your rim joists as the ledger board and install from there.

Product Questions

What is the UnderDeck Ceiling/Drainage System?

UnderDeck is a patented innovative maintenance free vinyl ceiling drainage system that attaches to the underside of your second level deck. It will return the once dark, dingy catch-all storage space for grass clippings and other debris to a dry, bright, clean area that family and friends can enjoy for years to come. It will be the most economical and valuable addition to your home's square footage. Your patio furniture will remain clean and last forever.

How does the UnderDeck system differ from other available products?

UnderDeck is constructed of maintenance free material that will not react adversely with the newly formulated pressure treating materials such as Amine Copper Quat (ACQ) or Copper Azole (CA). Unlike products constructed of aluminum, steel or tin. To find out more about the properties of these treatments, visit the Southern Pine Council. With UnderDeck's limited number of components, it is an intuitive and simple system to install. It is economical and aesthetically appealing. It will clearly add to the beauty, quality and life of your deck area.

What is the UnderDeck warranty?

UnderDeck warrants this product to be free from defects in material and/or workmanship of the product for a 15-year period after the date of purchase by a consumer. These warranties do not extend to secondhand homeowners. These warranties do not include damage to the product resulting in from an act of God, lightning, accident, misuse, improper installation or operation, or unauthorized repair or alteration. If the product should become defective within the warranty period, we will replace it free of charge with proof of purchase. The consumer’s sole remedy shall be repair or replacement as expressly provided above. IN NO EVENT SHALL UNDERDECK BE LIABLE FOR ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF THIS PRODUCT FOR ANY PURPOSE WHATSOEVER. Some states do not allow the exclusion or limitation of incidental or consequential damages, so the above limitation or exclusion may not apply to you. These warranties give you specific legal rights. You may also have other rights, which vary, from state to state. All implied warranties with the respect to this product (including merchantability) are limited to 15 years from the date of purchase.

Does UnderDeck only work with 16" joist spacing?

The UnderDeck components are available in standard sizes to accommodate 12", 16" and 24" on center joist spacing. If you have a unique opening on your project, the components can be easily trimmed to fit your application.

What colors are available?

Classic white and tan is offered on the Architectural Design Series. All colors utilize a low gloss on the gutters and a matte texture on the collector panels.

Can your ceiling be cleaned and what happens to the debris?

The system is very accessible to the homeowner. Limited amount of debris enters the system to begin with. However, due to the design, if debris enters the system through the gaps in the deck boards, it will slide down the collector panels and into the gutters and be evacuated through the pitched gutters. The system has positive drainage and will allow the water and debris to self clean. If, for some unforeseen reason, the system clogs, you can flush the system from the top with a garden house. If, for some reason, this flushing is not adequate, you can easily remove a section from below if required. Always remember the gutters and panels are removable if necessary.

Can the ceiling be removed?

Yes, and this is an important feature. It allows the deck deck to be repaired or to add lighting features etc. The ceiling can be removed with relative ease and re-installed without destroying the components.

Can I add ceiling fans, lights and porch swings under my ceiling?

Absolutely! The ceiling system unlocks and relocks back together, you can always get into the system to add gas lines etc. for years to come.

If I use a deck stain or a water seal treatment on my deck's boards above, will it damage the ceiling system below?

No. These are mild solvent-based products and will not damage or penetrate the exterior weatherable grade vinyl ceiling panels. If you scratch up a gutter during the installation, we recommend using lacquer thinner, a very strong solvent, to clean it up. The material is extremely damage resistant.

How long will the UnderDeck product last?

With 42+ mil thickness exterior weatherable grade vinyl with fungicides and anti bacterial additives the products are very durable.

Is UnderDeck affected by the freezing temperatures?

If the system is installed properly any water that makes its way to the gutters is evacuated in a mater of seconds and no water will remain to freeze.

What are the overall benefits of the UnderDeck system?

It protects the structural integrity of your deck. It is easy to install. UnderDeck allows you to create an indoor environment outdoors underneath your deck. You can install ceiling fans, lights, speakers, video electronics and furniture that will be safe from the elements.

What is UnderDeck made of?

UnderDeck is made of exterior weatherable grade vinyl with fungicides and anti bacterial additives. Never worry about maintenance or painting and UnderDeck will not rust.

Will chemical wood stains or treatments damage UnderDeck?

No. Staining or painting the deck above will not affect the UnderDeck. If you wish you can always take the components down and re-install them after your maintenance is complete.

Can lighting, fans, plants etc. be attached to the system? What about a screen enclosure?

Yes, you can include lights, fans and plants into you UnderDeck design. Many people even choose to screen in the area under their deck due to the increased time they spend in their newly created outdoor living area.

What about gutters and down spouts at the end of the joist gutters?

UnderDeck can be finished off as much as you like. Seamless gutters and downspouts are not necessary. However, most applications do utilize them.

Will the Underdeck system reduce the head room under my deck?

Slightly. Some products reduce the headroom by as much as 11”. Underdeck fits up into the joist space of your existing deck. Only a small portion of the gutters hang down approximately 2”. This only occurs repeatedly on the joist every 12”, 16” or 24”.

My joists are longer than 16 feet. Can I still use UnderDeck?

Yes, absolutely. Most decks with joists that are longer than 16', have a beam that runs perpendicular to the deck joists. At this beam, you end the system and install a common household rain-gutter to collect the water exiting the joist and boundary gutters. You then "start over" on the other side of the deck and continue the system. To prevent water from dripping down from the cross-beam, you will need to install two water diverters over the top of the beam. One of the diverters will direct water to the collector panel on one side of the beam and the other will direct water to the collector panel on the other side of the beam. If your cross-beam is on the same vertical plane as your joists, you will not need to install additional water diverters at the beam/joist intersection.

When estimating and ordering, it's easiest to think of your deck as two separate decks with a kit for each "deck". For example, if you have a deck with a joist length of 25' and a width of 30' and a beam that intersects at 14, you would order one 14' x 30' kit and a second 12' x 30' kit. UnderDeck is designed to be cut for a perfect custom fit. In this example, you would remove 1' from the gutters and panels of the 12' kit.

If you have a joist that is longer than 16' and is not interrupted by a beam, 18' and 24' extended length joists and boundary gutters are available. 99% of installations do not require extended length gutters. If you believe you require a gutter of this length, please contact us for pricing and availability.

My deck has double joists. Can I still use UnderDeck?

Yes -- if your deck has double joists (two joists that are connected side by side with lag bolts or screws), you can still use UnderDeck. If you are ordering a kit, please specify in the order notes the number of double joists that your deck has and we will contact you with an updated quote. If you are purchasing by ordering individual parts, simply order Double Joist Gutters instead of regular Joist Gutters.

What happened to the 10' and 14' gutters?

Underdeck 10' and 14' gutters are no longer available.


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