To extend your home and blur the line in between indoor and outdoors, adding a patio to your existing home might sound enticing. But unlike many other cities where building one is fairly straightforward, in Houston – with its frequent flooding events – building a patio can mean some extra legwork.
Before delving into the intricacies of building an open-air extension in a flood zone, it's crucial to clarify that the focus of this discussion revolves around structures that are open on more than two sides. It's important to note that different rules apply otherwise.
*Structures such as porches, patios, verandas, decks, and terraces could fall under this category.
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For homes located in a flood zone, an area that’s more prone to flooding from rainfall or storm surges, getting your extension approved can take longer than you might expect and it’s a likelihood you need to plan for. There are a few reasons why. First though, you should understand how flood zones work.
Layers of review
Inside flood zones are areas called conveyance zones. These are typically in the so-called 100-year floodplains, those areas expected to see a flood event every 100 years. In conveyance zones, water should flow across the land, or convey rainwater or storm surges from where they fall to the nearest river or other body of water.
In these areas, it’s important to allow for more land where water can soak into the ground. Your structure must also inhibit the flow of water as little as possible. Your property will be scrutinized for this, and you may need to add an area to hold water – a detention area for which you may also have to pay hefty fees, depending on your lot size (currently if over 15k sf) and proposed impervious coverage area or provide other ways for the water to flow through your lot.
Our Sager Project
You can identify whether the lot is situated in an area at risk for flooding by checking flood maps widely accessible online, including this site managed by FEMA.
If your home lies in the 100 year flood zone you’ll need Drainage and Mitigation Plans and if you are in a Conveyance Zone, you will need a Conveyance Report from a civil engineer before adding any structure. The plans must be reviewed by the Structural and Planning Departments and by the city’s Flood Management Office and Storm Drainage Office. Because the latter two offices are understaffed and overworked, it could take a few months to have your plan for a simple small patio reviewed. What’s more, the Flood Management Office must inspect the work. Their schedule can be difficult.
The City of Houston lists basic requirements for submitting a plan for an addition on its website. In addition to the city’s minimum requirements, you’ll also need a Topographic Survey if you’re in a floodplain. Outside of a floodplain, a boundary survey will suffice.
A trusted contractor
Once your designer completes plans for your addition, your contractor should pay the plan review fee, which is about $90, and submit plans online for review.
In our experience, plan review takes a minimum of two weeks for each review cycle, with a patio in the flood zone often taking twice as long as that, if not longer. Unfortunately, your contractor is at the whims of the city – they can’t do anything to speed up the process. However, an experienced contractor will have fewer mistakes with the first submission, making the process as smooth and quick as possible.
Once the city approves your plans, your contractor will pay the permit fee, which runs at around $205 and up, with an additional $370 for additions in the flood zone. Only then can your contractor start working on your patio.
If you’re interested in looking into adding a patio/porch for your existing or new home, start by finding a trusted contractor and make sure they have experience building in Houston and in a flood zone. It’s worth asking if they know the additional requirements before you get started. If they don’t know them off hand, chances are they may not be as experienced as they claim to be working in flood zones.
As you start planning for your patio in a flood zone, you’ll also want to prepare yourself for the additional costs. Added costs of building an addition in a flood zone include:
· Engineer Plans: $5,500 - $7,500 (Mitigation, Detention Plans and Conveyance Report)
· Permit Fees: $370
· Topographic Survey: $750-900
What We Learned From Working With Contractors
What about the design to withstand floodwaters?
Engineers must design the foundation (and any other portions subject to flooding) to withstand flooding loads and conditions.
1. Foundation
The most common type of foundation used is Pier and Beam, to allow the finished floor to be raised above the grade. Some designs will have a concrete beam around the perimeter with a framed or CMU wall, while some are completely open.
Flood vents must be incorporated into the foundation. The amount and size will depend on the type used and the footprint of the structure. Engineered Flood vents allow for fewer to be used but are more costly than plain openings or regular grates.
2. Frame
You’ll need to use flood-damage-resistant materials to create portions of the home below the design flood level. Flood-resistant materials that can withstand exposure to water and resist damage, such as pressure-treated lumber, steel, or concrete, are often used in flood zones.
In addition, each subcontractor will use specialty materials that help prevent damage from water. For example, framers will use specialized fasteners that resist corrosion/deterioration when exposed to water and for use with treated lumber. This helps ensure the integrity of the structure.
TIP:
We also recommend waterproofing the patio even if it’s covered. It will helps to prevent water buildup and potential moisture issues that can lead to mold or structural damage.
3. Electrical and HVAC.
All your electrical outlets and equipment (breaker panels, disconnects, generator etc.) and Air Conditioner must be at or above the Minimum Finished First Floor requirement for the structure. This type of equipment will require raised platforms with specific accessibility requirements that can be costly and visually obtrusive.
4. Exterior Grading
Grading plans for flood-prone areas need to incorporate proper slope and drainage systems to direct floodwaters away from the structure. The goal is to prevent water from pooling around the building's foundation.
5. Inspections
Additional foundation inspections, flood vent inspections, grading inspections, final elevation verifications.
While adding a porch in Houston, and especially in a flood zone, can take a few extra steps and it does come with added expenses, in the end you’ll be happy to have a cool getaway in your backyard that will also add value to your property.
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