How Do You Find Blocking on Construction Drawings?

THE FIRST THING TO UNDERSTAND

Blocking is usually hidden, waiting to be uncovered.

Sometimes a set of drawings makes blocking easy. You get a clear elevation, a detail, or even a dedicated plan that tells you what material goes where.

A lot of times you do not.

The blocking may be scattered all over the set. One condition is called out on an interior elevation. Another is buried in a wall type. A bathroom note may live near the front of the architectural drawings. The millworker may show another requirement only on the shop drawings.

That is why I do not think of blocking as a quantity I can find on one sheet. I think of it as investigative work.

Experience helps because you start recognizing the kinds of things that normally need support. A bathroom makes me think about grab bars, toilet partitions or urinal screens, mirrors, accessories, and anything else being mounted. Cabinets make me look for backing. A TV, sign, display, handrail, coat hook, fire extinguisher, millwork condition, glass track, or specialty door detail can all make me stop and investigate.

I am not only looking for blocking. I am looking for things that will need something solid behind them.

FOLLOW THE CLUES

Start on the floor plan, then follow the condition through the set.

My natural starting point is the floor plan.

I look at the room, the wall, the notes, and the objects shown in that area. If there is a section reference, I want to look at that section. A section may show plywood, dimensional lumber, metal backing, or another support that was never obvious on the floor plan.

Then I look at elevations. This is where a lot of the hidden conditions show up. The floor plan may show almost nothing, then the elevation shows cabinets, wall-mounted accessories, signage, millwork, or another item with a note to provide solid backing.

I also check the wall type. Sometimes the main wall type has a variation or subtype that adds plywood or another backing requirement at a particular condition.

Then there are the general notes and the information near the beginning of the drawing set. You can have a bathroom with no obvious blocking note in the room itself, then find a general requirement that says to provide backing for bathroom accessories.

There is no single perfect order because every drawing set is different. The important part is that you keep following the condition until the information stops being vague.

THE ARCHITECTURAL SET MAY NOT BE THE LAST WORD

Shop drawings and product information can change what the blocking actually needs to do.

Sometimes the architectural drawings do not show any blocking at all, then the millwork shop drawings show exactly where backing is required.

That immediately creates two questions.

First, what support does the actual installation need?

Second, whose scope is it?

If I am responsible for the blocking, I like coordinating with the people who are actually going to use it. A millworker may look at an architectural elevation and say their installation method needs the backing a little higher, lower, wider, or in another location. Bathroom accessory cut sheets can be useful for the same reason. If I can see where the mounting holes actually land, I have a much better idea of where the backing needs to be usable.

An elevation is often the clearest architectural view for height, but if drawings conflict, I do not like guessing. I check the approved shop drawings or product information when available, talk to the installer, and get the superintendent, architect, or other responsible project party involved when clarification is still needed.

The blocking has to work for the thing that is actually getting installed, not just look right on a drawing.

DO NOT LOOK ONLY AT NEW FRAMING

Existing walls can hide blocking scope too.

This is easy to miss during a takeoff.

You can have an existing wall that is already closed and still get a note to add backing for a new TV, sign, cabinet, accessory, or another mounted item.

That is a completely different condition from dropping a piece of plywood into an open stud wall while you are framing.

Now the work may involve opening the wall, coordinating access for an electrician or another trade, reinstalling insulation, installing the backing, then closing and patching the wall. Depending on the project, those pieces may be split between several scopes.

So when I see blocking on an existing wall, I do not just count a piece of material. I want to understand how the wall gets opened, who needs access, who owns the patching, what finishes are affected, and how far my responsibility actually goes.

INSTALLED DOES NOT ALWAYS MEAN USABLE

Blocking can be in the wall and still be in the wrong place.

I have been fortunate that blocking is one of the things I am always looking for, so completely forgetting it has not been the problem for me.

But I have seen another problem: the blocking was installed, and the accessory still missed it.

A bathroom is a good example. The drawing may give a finished-floor elevation for a grab bar or accessory, but the framing crew is standing on an unfinished slab. If the finished floor later gets tile, a mud bed, leveling, hardwood, or another buildup, the elevation you are measuring from can change.

If the floor buildup is not obvious, I would rather ask the superintendent what I should allow than quietly assume it.

I also like giving myself a reasonable target area where the documents allow it. If the backing is only a tiny strip placed exactly where I think the mounting point will land, a small field change can make that backing useless. A wider backing zone can give the installer some tolerance without turning every condition into a custom repair later.

The project requirements still control the material, size, assembly, and attachment. My point is simply that precision does not mean giving yourself zero field tolerance.

LEAVE YOURSELF A RECORD

Take pictures before the wall disappears, and give the picture a reference.

I like taking pictures of blocking before drywall goes up, especially in bathrooms, kitchens, and other walls with a lot going on inside the cavity.

The photo helps me remember where the blocking is, but it also helps show what else is around it. There may be plumbing, electrical, or other concealed work close to the backing. A photo is useful context later when somebody is planning an attachment.

But a picture with no scale can be almost useless. If there is no outlet, corner, or other obvious landmark, I may put a reference mark on the blocking and write a dimension from a wall or another fixed point. Now the picture tells me something more than, “there was plywood somewhere in this wall.”

A photo is still only one piece of field information. Fastener selection, required protective measures, concealed services, approved details, and the actual wall condition still need to be verified before installation.

FOLLOW THE PROJECT REQUIREMENT

The drawings should tell you what the blocking is. If they do not, make your assumption visible.

A lot of times the project documents tell you exactly what to use. It may be dimensional lumber. It may be 3/4-inch fire-retardant-treated plywood. It may be metal flat stock of a specified thickness. It may be another proprietary or project-specific support.

If the documents are silent and I need a number for pricing, my personal default is often plywood because it is familiar, easy to work with, and can be ordered pre-ripped to useful widths.

But that does not mean I silently decide plywood is structurally correct for every application.

If I carry an assumed backing condition, I want it written into the proposal. For example, I may state that the blocking price is based on a particular plywood thickness and that any different project requirement must be communicated before installation.

Previous jobs can give me a clue. If I have seen a similar accessory use a certain backing detail before, that may be a useful starting point. It is not proof that the same detail belongs on the current project. The current drawings, approved details, product requirements, and project direction still govern.

DO NOT PRICE ONLY THE MATERIAL

Blocking looks simple after the wall is closed. Installing it is not always simple.

Blocking is one of those scopes that can get treated like an afterthought because nobody sees it when the project is finished.

But somebody still has to receive the material, move it, store it, lay out every location, cut it, install it, clean up, and keep checking the drawings so it lands in the right place.

Plywood can involve full sheets, ripping, dust, cleanup, and fitting pieces between studs. Pre-ripping from the supplier can save field time, depending on the supplier and cutting cost.

In my experience, metal flat stock can be much faster to install than plywood when it is an appropriate specified system. It comes in usable widths and can run across the stud faces instead of being fitted piece by piece between studs. When I fasten flat stock, I like working the fasteners in one direction so I am not trapping bends or bubbles as I go.

Then there is congestion. A clean open wall is one thing. A plumbing wall packed with pipe, conduit, and wiring can turn a simple backing condition into a lot of fitting and notching.

Two blocking scopes can have the same linear footage and completely different labor.

TURN THE CONDITIONS INTO QUANTITIES

I like to organize blocking by the actual application, rip size, run, and number of rows.

Once I understand the conditions, I can finally turn them into material.

If it is plywood, I want to know the rip height or piece size, the length of the run, how many rows are required, and what waste or allowance makes sense. Cabinets are a good example because a detail may need an upper and lower row. That is not one run of blocking anymore. It is two rows along the same wall.

That is also why the BidSimp Blocking Calculator is set up the way it is. I built the calculator around the way I like to think through the takeoff: application, material, rip or piece size, run length, rows, and waste. The goal is to make the plywood, flat stock, or lumber quantity visible instead of burying blocking inside a rough allowance.

The calculator does not decide whether the backing is adequate. That still comes from the project information and the required installation. It simply helps turn a confirmed condition into a material quantity.

COORDINATE BEFORE THE WALL CLOSES

The cleanest sequence is not always the earliest possible sequence.

If my scope includes framing, blocking, insulation, and drywall, I generally like framing and blocking to happen together while the wall cavities are still clean and accessible.

Once insulation is already installed, going backward to add plywood can mean pulling insulation out, creating dust, disturbing the work, then putting everything back.

But blocking also cannot get in the way of work that still needs the cavity.

In a plumbing-heavy wall, it may make sense to let piping get established first so the backing does not block the route the plumber needs. Other walls may depend on electrical rough-in, specialty equipment, late shop drawings, or another coordinated condition.

Inspection requirements matter too. Some jurisdictions or project inspection sequences may require certain framing and backing conditions to remain visible together. That is something to confirm for the actual job rather than assume.

The goal is not “install blocking as early as possible.” The goal is to install it at the point where the information is reliable, the cavity is workable, the other trades are coordinated, and the inspection sequence still works.

MAKE UNCERTAINTY VISIBLE

If blocking is unclear during bidding, do not hide the assumption inside the base price.

Sometimes the contractor needs a price right away and nobody has a clean answer yet.

In that situation, I may carry an alternate for the blocking instead of pretending the drawings are clearer than they are. I can say, in effect, “Blocking is not shown clearly in the current documents. If it is required, add this amount based on the following scope.”

Then I outline exactly what I assumed.

That gives the contractor a number they can use, but it also gives us a record. If the alternate is approved, everyone knows what I carried. If the eventual requirement is different, the price can be adjusted based on an actual change in scope.

The same idea applies when shop drawings arrive late. If the new information simply shifts a backing location a little and does not materially change the labor or material, I may be able to accommodate it. If the late information adds a significant amount of backing or introduces a different condition than what was priced, that is something to discuss as an extra or change order.

The uncertainty around blocking may be unavoidable. The uncertainty in your proposal does not have to be.

FINAL FIELD CHECK

Before the wall closes, make sure somebody competent has eyes on the blocking.

When I am running work, I like doing a final pass before the wall disappears.

Sometimes I will walk the area and put Xs where blocking belongs. Sometimes I use a Sharpie on the studs. Sometimes, where it is appropriate for the finish and job conditions, I may use a floor mark. The point is to make the locations obvious enough that nothing quietly disappears.

I also like highlighting the floor plan and adding notes for the conditions that were particularly hidden or easy to miss.

That does not mean I want to spell out every screw for the foreman. You still have to delegate. A good foreman should be able to take the highlighted plan, follow the elevations and details, and understand the installation.

The level of field marking depends on the crew. If I have a foreman I trust who knows the drawings and the job, I can give them more room. If the crew is less experienced or the blocking is unusually complicated, I want more direct control.

I also want the board installation coordinated with the backing. Where the wall assembly or project detail requires the board to be fastened into the backing, that needs to happen correctly. Otherwise, tightening a finished accessory later can pull the board toward the backing and create movement or cracking. The actual wall assembly and board requirements still govern.

Either way, I do not want the drywall going up because everybody assumed somebody else checked it.