Patio Cover Attached to House: How to Build One the Wall Can Carry

A patio cover attached to a house looks like the easiest roof you can build: one slope, one wall, a beam and a few posts. The house does a lot of the work, which is why it is the common way to do it, and the wall is also the reason many of them go wrong. This guide shows where a ledger can go on the wall, what a solid roof adds that an open pergola does not, how the posts and footings are sized, and the order to build in.

We are not your building department or an engineer. Where a number comes from a code or a guide we say so, and where it is our designer’s own choice we say that instead.

Attached vs Freestanding: What a Lean-To Patio Cover Is

An attached patio cover is a lean-to: a roof with a single slope. The high edge sits on the house and the low edge on a beam carried by posts.

Why attach it

The house takes one whole side of the roof, so you need posts only on the outer side, and the wall helps hold the roof against sideways wind. A freestanding cover needs a frame that stands on its own in every direction, which means more posts, braces or deep footings.

What the wall has to do

The ledger takes the roof’s weight on the wall and its pull when the wind lifts the roof. Our designer checks every 1/2 in lag screw against the roof’s own loads, down, up, along the wall and away from it, with the fastener equations in Chapter 12 of the NDS 2018. For where a ledger may go, we borrow the deck rules in the IRC and the AWC¹ deck guide DCA6: pressure-treated lumber at least a 2x8, fastened into a band or rim joist, never through brick or stone veneer, hollow masonry, a bay window or a floor overhang. Those are deck rules and a roof is a different load, so we apply them by analogy and say so.

Attached or freestanding: how to decide

Attach it if you can answer yes to the ledger test in the next section. If you cannot, build freestanding and expect a bigger frame. Our pergola attached to house guide walks through the same decision for an open roof, and its wall test applies here too.

Tying a Patio Roof Into the House: The Ledger and Its Height

The ledger is a board bolted to the house, and the rafters hang from it. It has to land on framing that can take the load, and the height of the roof decides where that is.

A band joist or header at the right height

On a two-story house the band joist between floors sits well above a patio and is a good place for a ledger. Our designer does not borrow a deck table for the fasteners. It takes the roof’s worst gravity load (snow, drift, sliding snow or live load), the net uplift, and the wind along the wall and away from it, and checks each 1/2 in lag screw with NDS 2018 Chapter 12. A 1-1/2 in band is too thin for the full lag penetration the NDS counts, so the designer uses 375 lb across the grain, the value the IRC ledger table is built on. For our default 16x12 cover that comes out at lags every 20 in, staggered, with the worst check at 84% of capacity. Check the house, because we cannot see it.

The one-story problem

On a one-story house, the roof line is where the wall ends, and there is usually no band joist near the height a patio cover needs. What is behind the siding is wall studs. Neither the model code nor DCA6¹ has a table for a ledger on studs. Our designer lets you choose wall studs, and then it flags the plan amber on purpose. It sets two structural screws into every stud, 16 in apart, through the sheathing, and prints the load on each stud. For the default 16x12 cover that is about 251 lb per stud. You then compare that with the screw maker’s rated value and ask your building department whether the wall may carry the roof. This is our own method, not a code table.

Headroom is the limit on a low wall

Here is the honest part. The roof slopes down away from the house, so the beam on the outer side is lower than the ledger. If the ledger sits near 8 ft, which is where many one-story walls offer something solid, the beam falls well under the 6 ft 8 in clearance our designer wants under it. At a ledger 8 ft up and a 2:12 slope, our designer puts the underside of the beam at about 5 ft 5 in on an 8 ft projection and about 5 ft 0 in on a 12 ft one. At a ledger 10 ft up the same two covers clear 6 ft 8 in, at about 7 ft 4 in and 7 ft 0 in. Below 7 ft the plan also prints a comfort note. The fixes are a higher ledger, a flatter slope or a shorter projection, and some walls allow none of them. On a low wall a cover may not suit you, and it is better to learn that before buying lumber.

The ledger board itself

The ledger is at least a 2x8, and at least as deep as the plumb cut at the top of the sloped rafter, within 1/4 in, so the hanger has full backing. The second rule is our choice, borrowed from how a ridge board is sized. The rafters hang in slope-adjustable joist hangers, with a strap tie where they meet the beam, and both are rated for the uplift the plan prints.

Flashing at the wall

Water runs down the wall onto the roof, so the flashing must lap under the house wrap and siding above and over the roofing below. The usual minimum is 4 in up the wall and 4 in onto the roof, and that figure is our choice. For the ledger itself, the DCA6¹ flashing pattern applies: the siding comes off, the ledger flashing goes behind the wrap, and a drip edge sits below. The deck ledger board guide covers the fasteners and flashing in order.

Roof Slope and Roofing for a Patio Cover

A lean-to needs enough slope to shed water, and each roofing needs its own minimum.

Shingles

Asphalt shingles need at least 2:12. From 2:12 to under 4:12 they take two layers of underlayment. Our designer starts at 2:12 and builds the shingle roof on 15/32 in APA-rated sheathing, with 8d nails 6 in apart at the edges and 12 in in the field.

Metal panels

Lapped metal panels can go down to 3:12 with no sealant, or 1/2:12 with sealant applied along the laps, on the model code’s text. Many makers of exposed-fastener panels ask for 1:12 or more, so our designer turns the plan amber below 1:12 and tells you to read the maker’s guide. Panels go on 2x4 purlins laid flat at 24 in apart, or closer if the maker says so.

Polycarbonate and other panels

A lean-to patio cover with polycarbonate or fiberglass panels is a different product from the two roofs we model. Follow the panel maker’s slope and purlin spacing, and note that a translucent panel roof is still a solid roof for snow and wind.

Ice and drainage

The model code asks for an ice barrier where ice has formed before. An unheated cover rarely forms ice dams, so our plan asks your building department instead of deciding for you. Nothing in the designer is flatter than 1/4:12, the slope below which a roof has to be checked for ponding.

What a Solid Roof Adds: Snow, Wind and Uplift

An open pergola lets most of the snow and wind through. A solid roof does not, and that changes the posts and footings.

Roof live load and snow

Our designer uses 20 psf of roof live load for slopes below 4:12 and 16 psf from 4:12 up, from the residential code’s table for roofs. It works out snow from the ground snow load you enter, using the ASCE 7-16 method with a thermal factor of 1.2 for an open structure. The designer starts at a ground snow load of 20 psf. Your local value will differ, so ask your building department for it. We did not read the paid text of ASCE 7-16, so treat the snow arithmetic as ours and have it checked.

Dead weight

We take shingles on sheathing at 6 psf along the slope and metal on purlins at 3 psf. Those are rounded-up figures of ours, and they matter twice. They add to the load the frame carries, and they are the only weight that holds a roof down when the wind lifts it.

Wind uplift

A solid roof catches the wind from below. Our designer takes the suction for roof zone 2 in the residential code’s wind table, applies it to the whole roof area, and lets only 60% of the dry weight resist it. It starts at 115 mph. We use the same row at every slope and do not work out the separate pressure on an open-sided canopy, which is a simplification, so treat the uplift as a design estimate and have a local engineer review anything unusual.

Snow from the house roof

Snow can slide off the roof of the house onto a cover below, and it can drift against the wall. Our designer takes both into the loads from the house roof you describe: eave or gable, pitch, depth and how far the eave sits above the ledger. On the default 16x12 the sliding snow is the governing case. We worked from the published method for sliding snow and drift in ASCE 7-16, not the paid text, so have the numbers checked. Ask your building department whether it wants a different load. On a house with a roof directly above the patio this can be the biggest load of all.

Posts, Footings and Bracing for a Patio Cover

The outer side of the roof stands on a beam carried by posts. Two to four posts are normal, and the designer adds more when the footing or the base cannot hold the uplift.

Posts and the beam seat

Posts are 4x4 or 6x6 and the beam sits on a post cap or in a notch, never on a bolt through the side of the post. The rafters rest on the beam in a bird’s-mouth seat. We limit that cut to a quarter of the rafter depth and keep at least 1-1/2 in of bearing, and the designer checks the seat for crushing.

Footings sized for uplift

A footing is at least 12 in deep or below the frost line, whichever is deeper. The uplift is what makes covers expensive. On our default 16x12 shingle cover each post sees about 1,020 lb of uplift. The designer does not count friction from the soil, which is conservative, so it uses a straight round pier of concrete about 24 in across and 42 in deep at each of three posts, and the weight of the pier holds the roof down. Post bases are cast-in standoff bases, such as the Simpson² Strong-Tie CBSTQ, which the maker rates at 2,680 lb of uplift on a 6x6. Check the rating of whichever base you buy.

Bracing: shingle versus metal

A shingle roof on nailed sheathing can carry the wind on the beam back to the house wall, so our designer asks for no knee braces when its check passes. It treats the roof as a diaphragm that reaches out from the wall, with chords, end ties at the ledger and a collector, and checks the shear along the wall against 475 plf for 15/32 in sheathing with 8d nails, divided by 2.0 for allowable loads (AWC¹ SDPWS 2015, Table 4.2C). It also requires the cover to be no deeper from the wall than it is wide, because the roof is fastened along one line only. A deeper cover gets knee braces added for you. We read those values from excerpts and worked examples, not the full standard. Metal panels are not a diaphragm. A metal cover needs knee braces to the posts, or posts set in concrete, and the designer fails a metal plan that has neither. Braces are 2x6 at 45 degrees, and the foot of a brace is kept at least 6 ft 8 in above the patio.

Lumber and posts in the ground

The designer assumes pressure-treated southern pine. Posts set in the ground can rot at grade, and the guides we read advise against burying them, so a post base on a concrete pier is our default.

How to Build a Patio Cover, Step by Step

The order matters because the ledger and the footings are the two things you cannot easily redo.

Before you start

Confirm the wall, the permit and the setbacks. Find out what is behind the siding where the ledger will land. Have underground utilities marked.

Footings and posts

Dig to the depth on your plan, set the tube forms, pour, and set the post bases. Square the layout from the ledger line, not from the corner of the house, which may not be square. Set and plumb the posts, and fit the caps.

Ledger and flashing

Strip the siding where the ledger goes. Pre-drill the lag holes to the sizes the NDS and the screw maker give, fasten the ledger on the stagger and flash it behind the wrap before the rafters go up.

Beam and rafters

Lift the beam onto the caps and bolt it. Hang the rafters from the ledger hangers and tie them to the beam with the rated ties. Brace now if the roof is metal.

Roofing

Shingles go on sheathing, with the underlayment, drip edge and headwall flashing lapped as the maker says. Metal goes on purlins, with the closures and sealant. Finish the flashing against the wall last.

Do You Need a Permit for an Attached Patio Cover?

Maybe, and your city or county decides. An attached cover ties into the house wall and a solid roof carries snow and wind, which are the features that most often change the answer, so call before you buy lumber. We cover the exemption, what changes the answer and what to bring in our pergola permit and patio cover permit guide. The model code has an appendix for patio covers that applies only where a town has adopted it, and the guide says what we know about it. Our plan prints “local approval not checked” on purpose and never says no permit is needed. For what the finished cover costs, see covered patio cost.

Which Wall Can Take a Patio Cover?

A short test, in this order.

Is there solid framing at the roof height?

If you can confirm a band joist or header where the ledger will sit, use the band method. If not, ask whether wall studs are acceptable and who signs off on it.

Is the headroom enough?

Work out the beam height from the ledger height, the slope and the projection. If the beam falls under 6 ft 8 in, change one of the three before you go on.

Is there a roof above?

If the house roof drains onto the patio, ask your building department about the sliding snow and the drift. If it does not, say so on your application.

If the answers are no

Build freestanding. It costs more in posts and footings, but it needs nothing from the wall.