Steel Beam vs RSJ: What’s the Difference?

What Is a Steel Lintel?

A lintel is a structural member spanning over an opening such as:

• door;
• window.

Steel lintels can include:

• proprietary cavity-wall lintels;
• angle sections;
• other engineered products.

A lintel is not automatically the same thing as the large structural beam used for a major wall removal.

RSJ vs Lintel

The terms describe different things.

A:

lintel

describes the member's function over an opening.

An:

RSJ / UB

describes a type of structural steel member.

A UB can potentially act as a lintel.

But many lintels are not UBs.

Do I Need an RSJ for a Door Opening?

Not necessarily.

A normal doorway may use:

• proprietary lintel;
• concrete lintel;
• timber lintel in appropriate construction;
• other designed support.

A large bespoke steel beam is not automatically required.

Do I Need an RSJ for a Load-Bearing Wall?

Often some form of structural support is required when a load-bearing wall is removed.

That support might be:

• UB;
• UC;
• proprietary lintel;
• timber beam;
• reinforced concrete;
• structural frame.

The correct solution comes from the design.

Do I Need a Steel Beam for Every Load-Bearing Wall Removal?

No.

Steel is extremely common but it is not the only possible material.

Depending on:

• span;
• load;
• available depth;
• construction;

a designer may consider other structural solutions.

Can Timber Replace an RSJ?

Potentially.

Structural timber options can include:

• glulam;
• LVL;
• other engineered timber.

The required member may be deeper than an equivalent steel solution.

Fire, moisture, connections and available space also matter.

What About a Flitch Beam?

A flitch beam normally combines:

• timber sections;
• steel plate.

It can be useful where:

• structural strength;
• available depth;
• connection to timber construction

make it appropriate.

It still needs structural design.

Can Reinforced Concrete Be Used Instead?

Yes.

Reinforced concrete beams can support significant loads.

They are common in certain types of:

• framed construction;
• larger buildings;
• bespoke structural schemes.

For ordinary domestic knock-throughs, steel is often preferred because it can be relatively:

• compact;
• fast to install;
• readily available.

Which Beam Is Normally Used for a Kitchen Knock-Through?

Often a:

Universal Beam

is specified.

But there is no standard “kitchen RSJ”.

The beam depends on:

• opening width;
• joist direction;
• floor load;
• wall above;
• roof load;
• support conditions.

Which Beam Is Used for an Extension Opening?

Where the original rear wall is substantially removed, the structural solution can involve:

• one UB;
• two beams;
• UB with columns;
• goalpost frame;
• box frame.

Planning Portal notes that when a new or wider structural opening is formed into an extension, the remaining wall above needs to be supported, typically by one or sometimes more than one new beam.

Why Might an Extension Need Two Beams?

The geometry of the original wall and extension can require separate members to support:

• inner masonry leaf;
• outer masonry leaf;
• floor/wall arrangements.

Sometimes two beams may be:

• connected;
• bolted together;
• otherwise coordinated.

The structural designer determines the arrangement.

What Is a Goalpost Frame?

A typical goalpost frame consists of:

horizontal steel beam

supported by:

two vertical steel columns.

This can be required where:

• suitable masonry supports are unavailable;
• opening is large;
• reactions are substantial;
• structural stability requires it.

Does a Goalpost Frame Use UBs or UCs?

Potentially both types of section.

For example:

Horizontal Member

could be a UB.

Vertical Members

could be UCs.

But the exact sections depend on the structural calculation.

What Is a Box Frame?

A box frame is a more extensive steel arrangement that can include:

• upper beam;
• columns;
• lower member;
• structural connections.

It can be used where the structural analysis requires additional:

• stability;
• load transfer.

Is a Box Frame an RSJ?

No.

It is a structural system made from several members.

A homeowner might still casually say:

“We need an RSJ.”

But the design may actually involve:

• three;
• four;
• or more

steel elements.

Why Does This Matter for Pricing?

Because:

“One RSJ”

and:

“a structural steel frame”

are very different scopes.

The first might require:

• one beam calculation.

The second might require:

• beam design;
• columns;
• connections;
• foundations;
• frame stability.

This affects:

• structural-design fee;
• fabrication cost;
• installation cost.

What Is the Steel Construction Institute Blue Book?

The Steel Construction Institute produces recognised steel design resources commonly referred to as the:

Blue Book.

It provides structural-section information and design data for sections including:

• Universal Beams;
• Universal Columns;
• Parallel Flange Channels;
• hollow sections.

Structural designers use recognised section properties rather than treating all I-shaped beams as equivalent.

What Standard Defines Modern UB and UC Sizes?

The nominal sizes of standard:

• Universal Beams;
• Universal Columns;
• Parallel Flange Channels

are given in:

BS EN 10365.

This is why modern structural drawings use precise designations.

Why Does the Steel Section Have to Be Precise?

Because two sections that look similar can have different:

• flange thickness;
• web thickness;
• mass;
• stiffness;
• bending resistance;
• shear resistance.

The contractor therefore needs the exact section reference.

Can I Tell the Steel Supplier “Give Me a 203 Beam”?

No.

That is not specific enough.

There are multiple sections around that nominal depth.

You need the full designation, for example:

203 × 102 × 23 UB

rather than:

203 steel

or:

8-inch RSJ.

What About Imperial Beam Sizes?

Older drawings and existing buildings may contain historic steel described in:

• inches;
• older section designations.

This is particularly relevant when assessing:

• older industrial buildings;
• historic conversions;
• existing structural alterations.

A modern replacement should not be assumed equivalent simply because its outside dimensions are similar.

How Do You Identify an Existing Old RSJ?

It may require:

• measurement;
• examination of flange shape;
• section dimensions;
• historical section tables;
• sometimes opening-up.

The Steel Construction Institute maintains historic structural-steel information specifically because older sections differ from current standard UBs and UCs.

Why Would I Need to Identify an Existing Beam?

This can arise where:

• you are widening an existing opening;
• extending a loft conversion;
• connecting into existing steel;
• assessing previous structural work;
• regularising undocumented alterations.

The capacity of the existing member may need to be assessed.

Can an Existing RSJ Be Reused?

Potentially.

But the structural designer needs to establish:

• section;
• condition;
• loads;
• support;
• proposed new use.

Do not assume an existing beam has spare capacity.

Can I Drill Holes in an RSJ?

Not without checking.

Drilling through:

• web;
• flange;

can affect structural capacity.

The effect depends on:

• hole size;
• location;
• loads;
• section.

Service holes in structural steel should be coordinated with the design.

Can I Cut an RSJ Down?

Cutting its length as part of fabrication may obviously be required.

But altering the section by:

• cutting flanges;
• notching;
• removing part of the web

can significantly change structural performance.

Do not modify structural steel without design approval.

Can I Weld Something Onto the Beam?

Potentially, but connection details can affect:

• local stresses;
• structural capacity;
• fabrication requirements.

Welded structural connections should follow the design.

Does the Beam Need End Plates?

Not every beam does.

A simple beam bearing onto masonry may not require the same connection details as a beam connecting to:

• steel columns;
• another steel beam.

The fabrication depends on the structural arrangement.

What Is a Fin Plate?

A fin plate is one type of steel connection used to connect structural members.

It typically involves a plate and bolts.

It is more common in structural steel framing than in a simple masonry-bearing domestic beam.

What Is an End Plate?

An end plate is a steel plate welded to the end of a beam and used as part of a bolted connection.

It may connect:

• beam to column;
• beam to beam.

Again, it is a connection detail rather than a type of beam.

Does an RSJ Need Padstones?

Sometimes.

Where a steel beam bears onto masonry, the beam reaction needs to be safely distributed into that masonry.

A:

padstone

may be used.

Planning Portal notes that the existing wall below a beam bearing may need strengthening to prevent local crushing and that padstone size varies with the circumstances.

Does Every Steel Beam Need 150mm Bearing?

Planning Portal says that in typical domestic structural-opening guidance, new beams should normally have at least 150mm bearing onto their supporting walls.

But this is not a universal substitute for structural design.

The required support depends on:

• reaction;
• wall;
• masonry;
• beam;
• connection arrangement.

What Is a Beam Reaction?

The beam transfers load into its supports.

Those concentrated loads are:

reactions.

For example:

Floor + Wall

↓

B1 steel beam

↙︎  ↘︎

R1  R2

↓

Supporting masonry / columns

↓

Foundations

Why Does the Beam Type Affect the Supports?

Different sections can have different:

• weight;
• reactions;
• dimensions;
• bearing arrangement.

But support design depends primarily on the entire structural loading system rather than simply whether somebody calls the member an:

• RSJ;
• UB;
• UC.

Does a Steel Beam Need Structural Calculations?

For a bespoke structural steel beam supporting building loads:

normally, yes.

The calculation can establish:

• load;
• beam section;
• bending;
• shear;
• deflection;
• stability;
• reactions;
• supports.

Can I Just Use a Standard RSJ?

There is no universal standard beam for:

• 3m wall removal;
• 4m extension opening;
• kitchen knock-through;
• loft conversion.

Standard sections exist.

But their suitability is project-specific.

Does Building Control Need to See the Beam Calculation?

Building Control commonly requires sufficient structural information to demonstrate that a structural alteration satisfies Part A of the Building Regulations.

Relevant calculations are commonly submitted where bespoke steelwork forms part of the proposal.

Which Building Regulation Covers Steel Beams?

The principal structural requirement is:

Part A — Structure.

Approved Document A provides guidance for England covering structural matters including:

• loading;
• walls;
• floors;
• roofs;
• foundations.

Does Building Control Choose Whether I Need a UB or UC?

No.

Building Control assesses compliance.

The structural designer determines the proposed structural solution.

Building Control can:

• review;
• query;
• request clarification.

Do I Need Building Regulations to Install an RSJ?

Where the steel forms part of removing or altering a load-bearing wall:

normally, yes.

Planning Portal confirms that Building Regulations normally apply when an internal wall is:

• removed;
• altered;
• opened.

Does Installing a Steel Beam Need Planning Permission?

For an ordinary internal structural alteration to a house:

usually not purely because a steel beam is installed.

But separate planning considerations can arise for:

• listed buildings;
• flats;
• external alterations;
• extensions.

Planning permission and Building Regulations are separate systems.

Do I Need a Structural Engineer?

For bespoke steel structural design, competent structural-design input is normally required.

The Building Regulations focus on:

• competence;
• compliant design;

rather than saying every domestic beam must carry one particular professional title.

More complex structural systems may warrant specialist structural-engineering involvement.

Can My Builder Pick the Steel?

An experienced builder may understand common beam arrangements.

But:

installation experience

is not the same as:

structural-design responsibility.

The member should be selected from the actual structural calculation.

Can the Steel Fabricator Pick the Beam?

Only where the fabricator is genuinely providing competent structural-design services as part of its appointment.

A steel supplier simply supplying:

• cut steel;
• plates;
• fabrication

should not automatically be treated as the structural designer.

Should I Ask for an RSJ or a UB When Ordering Steel?

Use whatever exact designation appears on the final structural design.

If the calculation says:

B1 — 203 × 133 × 25 UB

that is what should be coordinated with the fabricator.

Do not convert it back into:

“a 203 RSJ.”

That loses important information.

Why Exact Terminology Matters at Fabrication Stage

At early enquiry stage:

“I need an RSJ”

is fine.

At fabrication stage:

“I need an RSJ about this big”

is not.

The order should define:

• section designation;
• grade where specified;
• length;
• plates;
• holes;
• connections;
• other fabrication requirements.

When Should I Order the Steel?

After:

1. Structural Design

Beam and supports determined.

2. Building Control Position

Relevant submission dealt with.

3. Site Dimensions Checked

Fabrication length coordinated.

Then:

4. Steel Ordered.

Do not select the steel from a general internet beam chart.

What If the Steel Supplier Says the Specified Beam Is Out of Stock?

Do not accept a substitute automatically.

Possible alternatives should be checked by the structural designer.

Another section might have:

• different depth;
• different stiffness;
• different connections;
• different structural properties.

What If the Builder Wants a Shallower Steel?

This can often happen when the proposed beam creates a visible downstand.

The structural designer can potentially consider:

• different UB;
• UC;
• alternative structural arrangement.

But it needs recalculating.

What Is a Downstand Beam?

A downstand beam projects below the surrounding:

• ceiling;
• floor zone.

This is often the simplest structural arrangement for a domestic opening.

What Is a Flush Beam?

A flush beam is integrated more closely within the floor zone so that there is little or no visible downstand.

This can require:

• joist trimming;
• joist hangers;
• complex connections;
• service coordination.

It is therefore often more complicated than a conventional downstand beam.

Is a UC Better for a Flush Beam?

Sometimes a UC's proportions may make it useful where depth is constrained.

But it is not an automatic solution.

The designer must check:

• strength;
• stiffness;
• stability;
• connections;
• supports.

Does a Steel Beam Need Fire Protection?

Often, yes.

Planning Portal notes that in a typical domestic load-bearing-wall alteration, steel beams should normally be protected to achieve the relevant fire resistance.

A common solution is suitable:

• plasterboard encasement.

Other systems can include:

• tested proprietary boards;
• intumescent protection.

The required solution depends on the project.

Is an RSJ More Fire Resistant Than a UB?

Not in any useful sense for a homeowner.

Both are structural steel.

Steel loses strength as its temperature rises.

The required fire resistance should be established through the Building Regulations design and appropriate protection.

Can I Leave the Steel Exposed?

Potentially only where an appropriate fire-protection solution demonstrates the required performance.

An exposed architectural steel beam should not simply be assumed compliant because it looks substantial.

What About Rust?

Internal structural steel in a normal dry domestic environment generally has a different corrosion exposure from external steel.

Where steel is:

• external;
• damp;
• embedded in problematic construction;

appropriate corrosion protection may be required.

The specification should suit the environment.

Does Every Beam Need to Be Painted?

Not necessarily with the same coating.

The appropriate treatment depends on:

• environment;
• fabrication;
• fire-protection system;
• specification.

Do not assume ordinary decorative paint is structural corrosion protection.

Is Galvanised Steel Better?

Galvanising can provide strong corrosion protection and is useful in certain environments.

But it adds:

• process;
• cost;
• detailing considerations.

It is not automatically necessary for an internal domestic beam.

How Much Does a Steel Beam Cost?

The beam price depends on:

• section weight;
• length;
• steel market;
• fabrication;
• drilling;
• plates;
• welding;
• delivery.

The steel itself is only one part of a load-bearing-wall project.

Additional costs can include:

• calculations;
• Building Control;
• temporary support;
• installation;
• padstones;
• fire protection;
• making good.

Is an RSJ Cheaper Than a UB?

This is not a particularly useful modern price comparison.

In most domestic enquiries, when people ask the price of an:

RSJ

they are actually being quoted for a current:

UB or another structural section.

The section:

• weight;
• length;
• fabrication

drive the actual price.

Is Steel Cheaper Than Timber?

It depends.

Steel can be more compact for high loads and long spans.

Engineered timber may sometimes be:

• lighter;
• easier to handle.

But timber sections can need greater depth.

The comparison should include:

• member cost;
• connections;
• installation;
• fire design;
• available space.

Which Is Better for a House?

There is no universal best material.

Steel is extremely common because it offers:

• high strength;
• relatively compact sections;
• widespread availability;
• predictable structural properties.

But the correct solution is determined by the actual project.

Example 1 — Kitchen/Dining Knock-Through

Homeowner says:

“I need an RSJ.”

Structural calculation determines:

B1 — UB

supporting:

• first-floor joists.

Builder orders:

• exact UB specified.

In normal conversation everyone may still call it the:

RSJ.

Example 2 — Large Rear Opening

Homeowner expects:

one RSJ.

Structural design identifies:

• B1 horizontal beam;
• C1 column;
• C2 column;
• foundation requirements.

The final structure is actually a:

steel frame.

This illustrates why the structural scope should be reviewed before pricing.

Example 3 — Restricted Ceiling Depth

A conventional UB creates too much:

• downstand.

The structural designer considers another section arrangement, potentially including:

• a UC;
• different beam configuration.

The selected member still has to satisfy:

• strength;
• deflection;
• stability.

Example 4 — Small Door Opening

Homeowner asks for an:

RSJ.

But the opening may only need:

• proprietary lintel.

Steel UB design may be unnecessary.

The structural solution should match the scale of the job.

Example 5 — Existing Victorian Beam

An older property contains an existing tapered-flange structural steel section.

The section may genuinely be an older RSJ/joist rather than a modern UB.

If its capacity is being assessed, historic section data can become important.

Do Old RSJs Need Replacing?

Not simply because they are old.

An existing structural beam can potentially remain if it is:

• adequate;
• in acceptable condition;
• suitable for the proposed loads.

A change in loading may require reassessment.

Can a Modern UB Replace an Old RSJ?

Potentially.

But the replacement must be structurally designed.

The outside dimensions alone do not establish equivalence.

What If I Am Buying a House With an RSJ?

Useful documentation can include:

• structural calculations;
• Building Regulations records;
• completion certificate;
• structural drawings.

If an opening appears to have been created without documentation, further investigation may be appropriate.

What If the Previous Owner Says “The Builder Put an RSJ In”?

That does not prove:

• correct beam size;
• adequate bearings;
• Building Control approval;
• structural calculation.

The important evidence is the technical and Building Control documentation.

Does an RSJ Need a Completion Certificate?

The beam itself does not receive a standalone completion certificate.

Where the work falls within a Building Regulations project, the Building Control process should be properly completed and the appropriate completion documentation obtained.

Does the Steel Beam Need to Be Inspected?

Building Control may wish to inspect relevant structural work before it is concealed.

This can include:

• beam;
• bearings;
• columns;
• fire protection.

Inspection requirements should be coordinated with the Building Control body.

Can I Box the Beam In Before Inspection?

Do not conceal structural work before any required inspection has taken place.

If Building Control cannot see important elements, it may require:

• photographs;
• opening-up;
• additional evidence.

What Does BuildRegs Call the Service?

For homeowners, the clearest wording is:

RSJ / Structural Opening Calculations.

This uses the term people actually search for while still allowing the final structural design to specify the technically correct member.

How BuildRegs Works

Step 1 — Upload Your Plans

Send:

• PDF;
• DWG;
• photographs;
• sketches;
• dimensions.

Step 2 — Structural Scope Review

The proposed opening is reviewed.

Step 3 — Fixed Quote

You receive a fixed price for the identified structural-design scope.

Step 4 — Structural Calculations

The suitable structural arrangement is calculated.

This may ultimately specify:

• UB;
• UC;
• another appropriate structural solution.

Step 5 — Digital Delivery

The agreed technical package is issued digitally for use in the Building Control process.

How Much Do Steel Beam Calculations Cost?

BuildRegs currently offers:

RSJ / Structural Opening Calculations

From £249

The final price is confirmed after the structural scope has been reviewed.

More involved designs can cost more where they include:

• several beams;
• columns;
• frames;
• connections;
• foundations.

Do I Need to Know Whether I Need an RSJ, UB or UC Before Uploading?

No.

That is the point of the structural design.

You only need to explain:

• what wall is changing;
• what opening you want.

Then provide whatever information you have.

The structural solution can be determined from there.

What Should I Upload?

Useful information includes:

• ground-floor plan;
• floor above;
• opening width;
• wall thickness;
• photographs;
• joist direction if known;
• roof information if relevant;
• planning/architectural drawings.

What If I Don't Have Drawings?

For a straightforward opening, the initial review may sometimes be possible from:

• dimensioned sketch;
• photographs;
• measurements.

More complex projects may require fuller technical information.

Frequently Asked Questions