Quick answer
A bottom seal is the compressible strip of rubber, vinyl or silicone attached to the bottom edge of a garage door so that it squashes against the floor when the door closes, blocking water, drafts, debris and pests.
DASMA defines the bottom weatherseal as an astragal or other weatherstrip attached to the bottom of a door to seal against the floor, and an astragal as a compressible or deformable seal on the door’s bottom edge.
Quick facts
The key facts about Bottom Seal, with sources:
- Bottom weatherseal (DASMA)
- Astragal or weatherstrip sealing against the floor 1
- Astragal (DASMA)
- Compressible or deformable seal on the bottom edge 1
- Astragal retainer (DASMA)
- Component on the bottom edge that holds the astragal 1
- Common profiles
- T-style, U/bulb-style, bead-style 6
- Materials
- Rubber, vinyl, silicone 6
- Typical replacement (one maker)
- Every 2–3 years, by climate and use 6
Key takeaways
- The bottom seal is the first line of defense against water, dirt and pests at the floor.
- DASMA calls it a bottom weatherseal or astragal.
- Most steel doors hold it in an aluminum or steel retainer channel.
- The profile must match the retainer: T-style, bulb or bead.
- No seal makes a door watertight; floor slope and thresholds help.
What a bottom seal is
DASMA defines the bottom weatherseal as an astragal or other weatherstrip attached to the bottom of a door to seal against the floor, and lists astragal floor rail, floor seal and thermal seal as other names for it 1.
Clopay describes the bottom seal as often the first line of defense against water, dirt and pests: it attaches to the lower edge of the door and compresses when the door closes, creating a tight barrier 6.
Garage floors are rarely flat. The seal has to fill dips and humps across the full width of the opening while still letting the door close fully. That is why it is soft and hollow, and why it wears out: every closing squashes it, and sun, cold and road salt slowly harden it.
Astragal: the trade word
In the door trade, the bottom seal is usually called the astragal.
DASMA defines an astragal as a compressible or deformable seal provided on the bottom edge of a door, and an astragal retainer as a component mounted to the bottom edge that holds the astragal in place 1.
On most steel sectional doors, the retainer is an aluminum or steel channel with one or two slots that the seal slides into.
Older wood doors and some one-piece doors use a flat astragal nailed or screwed directly to the bottom rail. Commercial doors may use heavier bulb or bead seals.
If a dealer asks what astragal you need, they want the retainer type and the seal profile. A photo of the door’s bottom edge, taken from the inside with the door partly open, usually answers both questions.
How it seals
As the door reaches the floor, the opener or your hand pushes the bottom section down the last fraction of an inch, and the seal flattens or folds to fill the gap.
A bulb profile, which Clopay calls U-style, compresses like a tube and is especially useful on rough or uneven floors 6. A T-style seal hangs as a fin or loop below a retainer and flexes to fill the gap.
Overhead Door, for example, lists a bulb-type bottom weather seal that it says guards against wind and rain on its fiberglass doors 7.
The seal works with the floor beneath it: DASMA recommends a slightly sloped lip or a notch in the slab so the door rests in a recess and water runs away 2.
- Door descendsSeal hangs below bottom section
- Touches floorSeal meets high spots first
- CompressesBulb or fin flattens 6
- Fills low spotsSeal conforms across width
- ClosedBarrier against water, drafts, pests 6
Source: [6]
Bottom seal profiles
| Profile | Description | Best for |
|---|---|---|
| T-style | Upside-down T that slides into a single or double channel 6 | Most residential doors; easy to replace 6 |
| U-style (bulb) | Tube or bulb that compresses 6 | Rough or uneven floors 6 |
| Bead-style | Rounded beads that snap into place 6 | Commercial, sometimes residential 6 |
| Flat nail-on | Strip fastened directly to the bottom rail | Wood and older doors |
Bottom seal materials
| Material | Pros (Clopay) | Cons (Clopay) |
|---|---|---|
| Rubber | Flexible, handles temperature changes, seals on uneven floors | Can stiffen and crack over time, especially in cold |
| Vinyl | Resists moisture and UV; lasts longer than rubber in sun | Less flexible in cold; may not seal as tightly on rough concrete |
| Silicone | Very flexible, holds up in heat and cold, resists cracking and fading | Usually more expensive; harder to find |
Example: matching a replacement seal
Before buying, measure three things at the bottom of the door with it open at waist height.
| Check | How | Why |
|---|---|---|
| Retainer type | Look at the channel: one slot or two | Seal beads must match the slots 6 |
| Slot width | Measure across the slot | Too wide a bead will not slide in |
| Door width | Measure the bottom edge | Cut the seal slightly long, trim after 6 |
| Floor gap | Look for daylight with the door closed | Large dips may need a bulb or threshold 6 |
- Single or double channel?
- Slot width?
- Door width?
- T, bulb or bead?
- Rubber, vinyl or silicone?
- Floor uneven?
Clopay suggests a little soapy water in the track if a new seal will not slide in 6.
Where you find it
Raise the door to chest height and look at the bottom edge. On steel doors you will see the retainer channel running the full width with the seal hanging from it. At each end is the bottom bracket, which holds the lift cable. The seal often runs under or beside the bracket.
Wood doors and some one-piece doors may have the seal nailed straight to the bottom rail instead of a channel. Commercial doors often add a heavier retainer and a deeper bulb or bead to cope with rougher floors and more traffic 6.
Replacing a bottom seal safely
Clopay’s guide treats bottom seal replacement as a do-it-yourself job: open the door, slide out the old seal, clean the retainer, cut the new seal a little long, slide it in, close the door to test, then trim 6.
It also says to call a professional if the door is especially heavy, has custom hardware or shows major alignment issues 6.
Two safety points matter. First, the bottom brackets at each end are under cable and spring tension.
Do not loosen or remove them to free the retainer; if the retainer itself must come off, that is a job for a trained technician. Second, a thicker seal changes where the door meets the floor.
After fitting it, run the monthly reversal test so the opener still reverses on an obstruction 4.
Leave the bottom brackets alone
The brackets at the bottom corners hold the lift cables under spring tension. Swapping the seal never requires loosening them. If it seems to, stop and call a technician.
Bottom seals and water
DASMA says it is common for rainwater to migrate past the bottom edge of exterior sectional doors, and recommends a slightly inclined lip or a rectangular notch in the slab so the door rests below the slab grade, with a slope of 3 to 5 degrees and a notch at least half an inch deep 2.
A seal alone cannot beat water running toward the door.
DASMA’s wind-driven rain guidance adds that sectional doors are not leak proof or watertight, and that an aluminum or rubber threshold and an enhanced bottom seal can be a great help 3. See threshold seal.
What a good bottom seal does
Limits
A bottom seal fills small gaps, not big ones. If one end of the door sits well above the floor, the floor is badly uneven or the door is out of level, and a technician should check cable lengths and the track.
DASMA notes garage doors are not watertight and building codes traditionally do not set water infiltration requirements for them 3.
What drives cost
No prices on this page. See the cost guide.
How to check your bottom seal
- Close the door and look for daylight along the floor.
- Feel for drafts on a windy day.
- Check for cracks, tears, flattening or brittleness 6.
- Look for water or leaves inside after rain 6.
- After any seal change, run the reversal test 4.
- Daylight at floor?
- Cracks or tears?
- Hard or brittle?
- Water inside?
- Pests or leaves?
- Reversal test passed?
Upkeep
Warning signs
A seal frozen to the floor can tear or make the opener strain; free it gently and keep the floor clear of ice and packed snow, especially where meltwater from a parked car refreezes overnight.
A seal that has slid out at one end, or a retainer that has rusted away, leaves a gap. A door that stops short of the floor after a seal change may need its travel limit adjusted, which should be followed by a reversal test.
Rules to know
No federal rule sets bottom seal performance on garage doors, and DASMA notes US building codes traditionally have not included water infiltration requirements for sectional doors 3.
The rule that does apply is the opener’s: after any change at the bottom edge, the door must still reverse on an obstruction as 16 CFR 1211 requires 5.
Bottom seal vs threshold seal
Myths
Climate
In cold climates, rubber can stiffen and crack, so silicone is worth a look. In hot, sunny places, vinyl resists UV better than rubber 6.
Replace or upgrade?
If the seal is cracked, flat or letting in light, replace it. If water still gets in, add a threshold and check the slab slope 2. For more on keeping the door in shape, see preventive maintenance.
Take a piece with you
Cut a short piece of the old seal and bring it to the store or dealer. Matching the bead profile by eye is much easier than by description.
Questions about Bottom Seal
What is a garage door bottom seal?
A compressible strip on the door’s bottom edge that seals against the floor. DASMA calls it a bottom weatherseal or astragal.
What is an astragal?
A compressible or deformable seal on the bottom edge of a door. DASMA calls this an astragal.
What is an astragal retainer?
The channel mounted to the door’s bottom edge that holds the astragal in place, per DASMA.
What type of bottom seal do I need?
Match your retainer: T-style for single or double channels, bulb for uneven floors, bead for snap-in retainers.
Rubber, vinyl or silicone?
Rubber flexes well but can crack in cold; vinyl resists sun; silicone handles extremes but costs more, per Clopay.
How often should I replace my bottom seal?
Clopay suggests most seals need replacing every 2–3 years, depending on climate and use.
Can I replace a bottom seal myself?
Usually, by sliding it out of the retainer with the door open. Never loosen the bottom brackets.
Why does water still come under my door?
Seals cannot stop water flowing toward the door. DASMA recommends a sloped lip or notched slab and a threshold.
My door will not close after a new seal. Why?
The seal may be too thick, per Clopay. Trim or choose a thinner one, then run a reversal test.
Do I need to test the opener after a new seal?
Yes. Run the reversal test so the door still reverses on an obstruction.
How do I stop my seal freezing to the floor?
Keep the floor clear of ice and snow, and a little silicone lubricant can help, per Clopay.
Sources
- DASMA Technical Data Sheet #160, Sectional Garage Door Terminology, retrieved .
- DASMA Technical Data Sheet #197, Water Infiltration Under the Bottom of a Sectional Door, retrieved .
- DASMA Technical Data Sheet #1503, Wind-Driven Rain and Sectional Garage Doors: Reasonable Expectations, retrieved .
- DASMA Technical Data Sheet #364, Installation Location of Photoelectric Sensors on Residential Garage Doors, retrieved .
- 16 CFR Part 1211, Safety Standard for Automatic Residential Garage Door Operators (eCFR, current), retrieved .
- Clopay, Garage Door Seals: A Buyer’s Guide, retrieved .
- Overhead Door, Impression Collection Fiberglass Garage Doors, retrieved .
Expert review
Written by the HyreGarage Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Definitions from DASMA TDS-160; water guidance from TDS-197 and TDS-1503; profiles, materials, install and upkeep from Clopay’s seal guide; reversal test from TDS-364.
Suggest a correction. We fix errors and say what changed.