Artificial grass installed in Seattle and surrounding areas will sit on a foundation that determines whether it drains well, stays flat, resists odor and lasts through wet winters and dry summers. This guide walks a homeowner through the layers beneath the turf: the infill that props up the fibres, the base rock and compaction that prevent settling and puddles, and the drainage rates that matter most when rain falls for weeks or a dog area turns to mud. You will learn what to ask for in writing, how to spot a shortcut installation, and why the same turf can fail on poor base prep and succeed on a properly built foundation.
Whether you are planning a residential yard, a pet area, a patio or balcony, or any other application, the principles are the same: good drainage starts below the surface, and a written specification protects you from guesswork and shortcuts.
Turf Infill Options: Silica, Coated Sand, Zeolite and Envirofill
Infill is the granular material worked into the turf after it is laid. It serves multiple purposes: it props up the synthetic fibres so they stand upright and feel natural underfoot, it protects the backing from ultraviolet light, it adds weight so the turf stays in place, and it plays a role in how quickly water drains through. The most common infill is silica sand, a fine mineral that is inexpensive and effective as a basic ballast. Coated sand is silica sand that has been rounded and often coloured to match the turf blade or to reduce glare and heat reflection. Zeolite is a porous mineral that absorbs and neutralizes odors, making it popular for pet turf and dog runs where urine breaks down into ammonia.
Antimicrobial and cooling coated infills, sold under brand names such as Envirofill, combine a mineral base with a coating designed to inhibit bacterial growth or to reflect heat. These products are sourced for specific applications where odor control or temperature management is a priority. Crumb rubber, made from recycled tires, is standard in sports fields and synthetic turf courts where impact absorption is essential, but it is rarely used in residential yards because of its heat retention and maintenance demands. The choice of infill depends on your use case, your budget, and the turf product itself. Ask your installer what infill type and amount they specify in writing before the job begins.
How Much Infill Artificial Grass Needs, and Why
Infill quantity is specified in pounds per square foot, and it varies depending on the turf product, the pile height, and the intended use. A typical residential turf might call for 2 to 4 pounds per square foot, while a pet area or a putting green may need more. The infill props the fibres upright, protects the polyethylene or nylon backing from sun damage, adds ballast weight, and influences drainage performance. Too little infill is a common shortcut in cheap installations: the turf may feel thin underfoot, the fibres flatten prematurely, the backing degrades faster, and drainage can actually slow because the infill is insufficient to maintain the pile structure.
The right amount of infill is not a guess. It is a specification that depends on the product data sheet and the conditions of your yard. When you get a quote or a proposal, ask for the infill amount in writing, measured in pounds per square foot. If an installer cannot or will not give you this figure, that is a red flag. The infill will be spread and power broomed into the turf after installation to ensure even distribution and proper fibre stand.
What to Put Under Artificial Grass for Drainage
The layers beneath artificial grass are as important as the turf itself. Start by removing the existing lawn, old turf, and roots. If the yard is overgrown with moss or compacted from years of foot traffic, excavation clears away the debris and gives you a clean slate. Next, grade the site so water runs away from the house, the pool, and any structures. In Seattle yards, which often slope steeply or hold water in low spots, this step is critical. A weed barrier (usually a landscape fabric) may be laid to prevent weeds from growing up through the base, though it is not always necessary and depends on site conditions. On top of that, install a free-draining base of decomposed granite or crushed base rock, typically 2 to 4 inches, and compact it firmly in lifts using a plate compactor so it does not settle later and create dips.
For residential yards, patios and balconies, and pet areas, an optional draining underlay or cushion pad may be added on top of the compacted base. This pad provides comfort, additional drainage, and some insulation. On concrete, decks, or balconies, never glue turf flat to the slab without a draining pad and edge drainage: water will pool under the turf, the backing will rot, and odor will build. The turf is then laid on top, seams joined, edges secured, and infill worked in and power broomed.
Base Prep on Seattle Soil: Excavation, Base Rock and Compaction
Seattle's soil is predominantly glacial till and clay, which holds water and drains slowly. In many yards, especially on the slopes that characterize Ballard, Capitol Hill, Queen Anne and the Eastside, you will find hardpan or compacted layers that shed water rather than absorb it. Poor drainage in the base is the most common cause of artificial grass failure in this region: water pools under the turf, the infill becomes saturated, odor develops (especially in pet areas), and the backing breaks down. A properly prepared base prevents all of this. Excavation removes the old lawn and roots and establishes a level or gently sloped surface. The site is then graded so water runs away from the house and any pool or structure, typically at a fall of 1 to 2 percent. The base material, usually 3 to 4 inches of decomposed granite or crushed base rock, is laid and compacted in lifts using a plate compactor. Each lift is compacted firmly before the next is added. This compaction is not cosmetic: an uncompacted base settles over time, creating dips and low spots where water collects, and the turf sags with it.
On sites with severe drainage problems, such as a low spot that holds water after rain or a yard with no outlet, base prep alone may not be enough. In those cases, the real issue is site drainage, and it should be addressed before turf is installed. If a yard has a persistent water problem, we will either recommend a solution (such as a French drain or a swale to redirect water) or decline the job. The turf itself is excellent, but it cannot overcome a broken foundation.
Artificial Grass Drainage and Underlay: Perforated vs Fully Permeable
Artificial grass drainage is measured in gallons per hour per square foot, a rate that tells you how fast water passes through the backing. Most residential turf has a perforated backing that drains quickly, typically 15 to 30 gallons per hour per square foot. Some products offer fully permeable backing that drains even faster. The difference matters most in heavy rain or in a pet area where urine and water volume are high. In Seattle, where November through March brings weeks of steady rain, the real test of drainage is not the turf itself but the base beneath it. A fast-draining turf sitting on an uncompacted or poorly sloped base will fail: water will not drain through the base, it will pool under the turf, and the yard will become a bog.
Underlays and drainage pads are optional layers placed between the base and the turf. They are most useful on hard surfaces such as concrete, decks, or balconies, where they create a gap for water to flow and escape at the edges. On a properly prepared soil base, an underlay may not be necessary, but on a patio or a rooftop, it is essential. When you request a quote, ask your installer for the drainage rate of the turf in writing, the type of backing, and whether an underlay is recommended for your site. Do not rely on guesses: the spec should be clear.
Seams, Nails, Edging and Power Brooming
The finishing details of an installation reveal whether the work is done carefully or cut short. Seams, where two pieces of turf meet, are the most visible joints. A professional seam is joined with seam tape and adhesive, with the grain of the turf blades aligned so the seam is nearly invisible when viewed from above. The tape is laid under the joint, adhesive is applied, and the edges are pressed together firmly and allowed to cure. Nails or staples secure the turf to the base, spaced at the correct intervals (typically every 6 to 12 inches around the perimeter and along seams) so the turf does not shift or wrinkle. Edges are finished with bender board or a secured perimeter so the turf does not fray or curl up. Where turf meets pavers, a patio strip, or a cool deck, the cut should be tight and clean.
After the turf is laid and fastened, power brooming is the final step. A power broom stands the fibres upright, spreads the infill evenly, and gives the surface a natural, finished appearance. A visible seam, lifted edges, wrinkles, or fibres that remain matted are signs that the installation was rushed or done without proper technique. If you see these issues weeks or months after installation, the work was not done to standard. When you get a proposal, ask whether seams will be taped and glued, how the edges will be finished, and whether power brooming is included.
What a Written Turf Spec Should Include
Before you sign a contract or agree to a price, demand a written specification from your installer. This document protects you by making clear exactly what will be installed and how. A complete spec includes: the turf product name and fibre type (polyethylene or nylon), the face weight in ounces per square yard, the pile height in millimeters, the backing type and drainage rate in gallons per hour per square foot, the infill type and amount in pounds per square foot, the base depth and material (decomposed granite or crushed base rock), the compaction method and standard, whether a weed barrier will be used, the seam method (taped and glued), the edging treatment, cleanup and haul-off of old turf or debris, and the workmanship warranty period. A workmanship warranty typically covers the installation for one to three years against seam separation, wrinkles, and edge lifting. Manufacturer warranties on the turf product itself are separate and are the responsibility of the turf maker, not your installer.
A written spec is your proof that you hired a professional who knows the product and the process. It is also your defense if something goes wrong: you can compare what was promised to what was delivered. If an installer will not provide a spec in writing, or if they offer only a price per square foot without product details, keep looking. We measure every yard on site and provide a detailed estimate and spec. Call for a free estimate, or visit our pricing page to understand how we work.