Standard, Bespoke or Loose-Fit Drainage Stacks: Choosing the Right Approach

The wrong drainage stack strategy usually shows up later: unresolved risers, site adjustments, excess loose material, delayed installation and installers having to solve coordination issues under pressure.


The decision should not start with “prefabricated or traditional?”


It should start with three questions:


How repeatable is the layout?
How coordinated is the design?
How stable is the project?


Where layouts repeat and the design is fixed, standard prefabricated stacks can reduce site work and make installation more predictable.


Where the building is complex but well coordinated, bespoke prefabrication can resolve difficult areas before they reach site.


Where layouts are still changing, loose-fit installation may still be the most practical choice.


“We often see projects default to one approach before the layout, repetition and programme have been properly reviewed,” says Lloyd, PIPEKIT’s Design and Technical Support Manager. “The best outcomes usually come from understanding the project first, then deciding where standard, bespoke or loose-fit systems genuinely add value.”


This guide is about choosing the right approach for the building, not forcing prefabrication where it does not belong.


What PIPEKIT Looks At First


Before recommending standard, bespoke or loose-fit drainage stacks, PIPEKIT looks at the project conditions:

  • Are risers repeated across floors or plots?
  • Are bathroom and kitchen layouts consistent?
  • Are connection points fixed?
  • Is MEP coordination mature enough to manufacture from?
  • Is riser space restricted?
  • Are services congested?
  • Are layouts frozen or still changing?
  • Where are late changes most likely?


The answers usually point to the right approach.


Standard stacks suit repetition.
Bespoke stacks suit coordinated complexity.
Loose-fit systems suit areas that still need flexibility.


“There are projects where you simply don’t have all the answers early on,” Lloyd explains. “That’s where flexibility still matters.”

Pipekit HDPE Drainage Stack Type 05 Kitchen / Utility in black
Pipekit HDPE Drainage Stack Type 05 Kitchen / Utility
Pipekit HDPE Drainage Stack Type 03 Bathroom / Shower Room Left Handed in black
Pipekit HDPE Drainage Stack Type 03 Bathroom / Shower Room Left Handed
Pipekit HDPE Drainage Stack Type 01 Multi Boss Bathroom / Shower Room in black
Pipekit HDPE Drainage Stack Type 01 Multi Boss Bathroom / Shower Room
Pipekit HDPE Drainage Stack Type 00 Stack Top Section in black
Pipekit HDPE Drainage Stack Type 00 Stack Top Section

Loose-Fit Systems - Best where flexibility matters most


Loose-fit systems still have a clear role where the design is moving or site conditions are difficult to predict.


They allow installers to adjust pipework, respond to late changes and work around access restrictions.


Loose-fitcan be the right choice where:

  • layouts are still changing
  • riser positions are not fully resolved
  • service routes are still being coordinated
  • access affects sequencing
  • late changes are likely


“Loose-fit gives installers freedom to adapt,” Lloyd explains. “On certain projects, that flexibility is worth more than the efficiencies of prefabrication.”

The trade-off is control. Loose-fit installation relies more heavily on site labour, supervision and installer consistency.

That does not make it wrong. It means it should be chosen deliberately, not left as the default.


Standard Prefabricated Stacks - Best where repetition drives the project


Standard prefabricated stacks work best where the same drainage layout repeats across floors, plots or risers.


They are particularly suited to:

  • student accommodation
  • hotels
  • build-to-rent schemes
  • social housing
  • high-rise residential
  • repeated bathroom or kitchen layouts
  • consistent riser positions


Where the same detail appears again and again, there is little value in measuring, cutting and resolving it repeatedly on site.


“When you’re dealing with repetition, there’s no benefit in redesigning the same stack multiple times,” Lloyd says. “Standardisation allows the design team to coordinate once and apply it consistently.”


The value is not simply offsite manufacture. It is repeatability.


A known arrangement can be coordinated, fabricated, tested and installed consistently across the building.


“Where layouts repeat, standardisation removes a lot of unnecessary complexity,” Lloyd adds. “You’re creating a process that can be repeated reliably across the building.”


Standard stacks are strongest where the layout is repeatable, the design is coordinated and the programme is stable.

Bespoke Prefabricated Stacks - Best where the building drives the solution


Bespoke prefabrication is useful where the building is too complex for a standard arrangement, but coordinated enough to resolve before installation.


This may include:

  • irregular geometry
  • congested service zones
  • restricted riser space
  • mixed-use developments
  • complex MEP coordination
  • plant areas
  • non-standard interfaces

“Bespoke works best when coordination is driving the solution,” Lloyd explains. “You’re resolving complexity before it reaches site.”

Bespoke stacks can reduce site adjustment in difficult areas, but they depend on reliable information.

If the design is still changing, bespoke manufacture can lock the project into a solution too early.


The same test applies:


Is it repeatable?
Is it coordinated?
Is it stable enough to commit?


Most Projects Need a Blend


Most projects do not sit neatly in one category.


A residential scheme may use standard stacks through repeated accommodation floors, bespoke assemblies in plant or mixed-use areas, and loose-fit systems where flexibility is still needed.


“The projects that run best are usually the ones that stay pragmatic,” Lloyd says.
“Standardise where it creates value, but don’t force it where it doesn’t.”


The aim is not to maximise prefabrication.


It is to choose the right drainage strategy for each part of the building.


Choosing the right stack strategy starts with understanding the building.


The impact shows up during delivery: coordination, sequencing, our, logistics, quality and risk.


Part 2 looks at where those decisions affect the site programme.